Of course should have returned the money, just as if you were shorted you would expect it to be corrected. as far as other comments about not being able to make change, using a calculator etc, and still screwing up... I was at the dentist several years ago, paid cash for a cleaning, receptionist takes out a calculator to do the math, it's wrong...in my favour. I tell her that there's a mistake , she apologizes, does her thing with the calculator again and wants to give me even more money back. I tell he that it's still wrong, she calculates again and says, "No, that's the right amount" I knew in my head that it was wrong but what can you do when she says it's right, and she says it with attitude like I'm the asshole...if she knew simple math it would have told her she was wrong
I worked in retail while going through high school, the cash register wasn't an electronic with change calculated and you always counted the change back to the customer . In other words say the bill is $ 12.67 and customer gave you a 20, you counted the change back to the customer "that's $12.70, $12.75, $13.00, $15.00 and $20.00 Long gone are those days . Now often I find you just get handed the change