I'm overly cautious when it comes to the IRS, so years ago I paired up bitcoin purchase and sales in a spreadsheet, and listed the buy/sell dates separately. My goal was to make it easy for me to match what I wrote with the records I kept. Note when you purchase something with bitcoin, you are "selling an asset" (bitcoin) in the IRS' view. When bitcoin leaves your possession, I'd report the value at the time it did so. You might also want to print any records of the sale to PDF, and keep that with your tax returns.