Actually, I just fixed a bug in the invoice printing routine.
I'm usually around the place for bigger events for general troubleshooting, which does include fixing bugs. In this particular case, I was subbing in for the real cash register personnel to give them a little break when I noticed a printing error on an invoice I just printed for a customer who wanted to pay his stuff.
I asked him whether he had 2 minutes? I'll fix that." He goes, he doesn't actually mind the error, but he'll wait two minutes.
So I dive into good old Turbo Pascal and fix the error, recompile, cancel the bad invoice and reprint: Voila, bug fixed.
For more relevance I do usually code at that place back to back with the cash register personnel, and they'll suggest improvements.