I have a UMB HSA as well. You won't have to show a receipt unless you're audited. At least with mine. However, legally, you should keep aside the amount you 'cashed' out and when you file your taxes, there's a question that asks if all proceeds from your 1099-SA were used for a approved expense.
But really, 27 bucks? I'm sure you'll find a place to use that before the end of the year. If you go to a CVS, you'd be surprised at the HSA eligible items.