I get the look every few months, as my roommate pays me his share of rent in cash. I have a credit union account than I only keep for depositing this cash (my actual bank is etrade, so no branches), and I hold some savings in it to avoid fees. Every few months when I have enough to bother with I'll take a stack of cash, deposit it, then immediately transfer it back out to my investment account. I usually go Saturday mornings and I'm dressed in cargo pants, tshirt, and motorcycle gear. Every time I hand it to them they go 'that's a lot of cash...' *suspicious look*. This next trip is going to be $5500 cash, biggest yet, looking forward to the reaction.
Just in case you don't know already: eventually a cash deposit will either be large enough that the bank personnel are mandated by law to fill out a report form for the IRS, or, even if you stay under the cap, they can flag you to the IRS anyway if they feel like it for "structuring" cash deposits to avoid triggering a report. Basically you do not want to garner any bank or IRS attention for making cash deposits, even though the funds are legally obtained and even though you are planning to pay all of the tax you owe on this income. There was a time just in the past few years when the IRS routinely seized and held huge sums of money from folks in the name of "something here could be illegal, so we're going to seize all of your money and hold it for years until it is all sorted out by us (if we get around to it.)" The IRS came under a lot of fire for that because they did it to people like restaurant owners who just happened to have a lot of legit cash from their businesses, so as far as I know they have mostly stopped, but it could start up again any time.
Please note that if they decide to start tracking your cash deposits, you only have to deposit $10K IN AN ENTIRE YEAR for it to count as reportable. I've put the link below.
You would be wiser to either use the cash from your roommate directly as your "walk around spending money" or make the small deposits regularly as you receive the money so that you are not raising their eyebrows at the bank . . . ever.
From the IRS reporting regulation (https://www.irs.gov/publications/p1544/ar02.html)
"Over $10,000,
Received as:
One lump sum of over $10,000,
Installment payments that cause the total cash received within 1 year of the initial payment to total more than $10,000, or
Other previously unreportable payments that cause the total cash received within a 12-month period to total more than $10,000"
Let me put some fears to rest. I use to work at a bank. I can confirm that a $10,000.01 cash lump sum will trigger a CTR. It's a form the teller fills out when you make the deposit or withdrawal. I was a banker, not a teller, but I did have to fill one out once. It is pretty painless. The form itself doesn't raise any eyebrows, it happens, no biggie. We had a few clients with cash heavy businesses who had to fill it out every week. They didn't have any problems. When it will raise eyebrows is if your tax forms at the end of the year show something very different. A restaurant reporting $5,000 in cash sales on their tax forms, but then $100,000 in reportable cash deposits at the bank is asking for an audit.
RyanAtTanagra is probably fine based on what has been said. No one cares that he deposits a few thousand every few months. The teller is probably commenting on it to try to start a conversation. They are trained to try and start conversations with people, and learn more about you so that they can position other products of the bank. "This is a lot of cash," will normally lead to, "Why don't you have a savings account?" "Oh, your savings is at E-trade, nevermind." If she is actually suspicious of him making those deposits then that is very odd. People make large cash deposits at banks, and on a Saturday everyone dresses casual.
If your various transactions throughout the year put you over $10,000, no one notices or cares. I have never seen or heard of this happening. Installment payments refers to someone giving you exactly X amount on X day of each month, and that equaling more than $10,000. Example: you sell a car/house/business and the buyer is making cash installment payments. The IRS wants to know about that because all the installments add up to one initial transaction that was greater than $10k, but that is really for you to self report. The bank isn't reporting that unless you do something suspicious to raise red flags. Depositing a few thousand every few months isn't suspicious.
Trying to structure your transactions to avoid filling out the form will get you significantly more unwanted attention than if you deposited more than $10k and completed the form. I'll wager the businesses who had their money frozen were trying to structure their transactions to avoid the $10k threshold, OR they weren't reporting their full cash sales on their taxes. From the bank & IRS's point of view structuring transactions to avoid the $10k threshold looks very similar to structuring money for money laundering purposes. Regular transactions for $9,900 for instance will raise red flags. The craziest case I heard of was a guy making large cash deposits at multiple banks everyday. Note, these weren't branches of the same bank, they were separate banks. Example: Bank of America and Wells Fargo. How did he get flagged? One of the tellers at bank A that he normally dealt with quit to take a job at Bank B. She quickly realized the regular deposits were more than $10k a day...
EDIT: @RyanAtTanagra: Motorcycle gear? When do you take your helmet off? Someone walking into, or even approaching a bank with their face hidden will automatically raise the blood pressure of every teller. ;-)