First: I'm not sure if I should post this as a bug or a suggestion. Strictly speaking, it's a bug. But not one that breaks the game or affects gameplay. That being said:
For .. reasons, I gave a customer the change in 1c coins. 1500 coins - and they clipped through the roof into the upper floor.
Like I said: Probably doesn't need changing, not many people will encounter that. And it's just fun if they do, imho. But if you want to change it, you could limit the amount of coins that player can give back.