Are you talking about after you have all ready given someone money for the purchase and they punched it into the computer and started the transaction/printed the receipt? If so, I would give you a deer in the headlights look too. I used to hate mother****ers who did that when I was a cashier. It didn't have anything to do with knowing how to add or subtract, but the amount I give back matching what the receipt says.
Also, why not give the change right away ? Either give it up front or take the change you deserve.
It may be funny to you, but it can be quite annoying. Old people are the worst about it.
Just trying to give some perspective from a former cashier. That was my entry position when I first started working at Home Depot. You may not be the guy I'm talking about in my post.

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