had a customer earlier who prepaid for gas and pressed $20 for cashback, so I hand her the money; cue "oh, I didn't mean to hit $20, I don't want it!" and she leaves to deal with the gas without taking the money, even though her card definitely got charged for it.
so what the hell do I do with this $20 sitting on my till then? I don't want to keep it, because it's not mine, but I can't put it back because it'll screw over the totals later.