One time a teller put too much money in the envelope at a drive through. I didn't realize it until I got home, which was at closing time. I reported it right away, and happened to get the same teller when I called. She thanked me, and said I saved her a major headache and maybe her job. I have given money back to cashiers who gave me the wrong change. Had I done otherwise, I would still have it on my conscience.
Mom always told us, 'a thief is a liar, and a liar is a thief.'