Adventures in Grocery Checking: Do The Math

Basic math skills are lacking in Sheboygan, as you can see from the following real life examples:

Me: That'll be $10.50 please.
Old Lady: But the sign says 2 for $10.
Me: ...right, they are, and there's 50 cents sales tax.
Old Lady: Well the sign didn't say that.
Me: Laundry detergent isn't food, so it's taxed.
Old Lady: The sign didn't say that.

Me: And $20.81 please.
Woman: Can I write a check for over?
Me: Yep. Up to $30 more.
Woman: I only want $10, so how much would that be then? 20.81 plus 10...what would that be?

Me: Your total is $24.13.
Woman: *to self* Hmm...so that'd be about 50 then, right?
Me: You need cash back?
Woman: Yeah, I only want $5 back so how much would I write it for? $50?
Me: ...No, you'd write it for $29.13.
Woman: Oh.

Me: How many donuts are in here?
Woman: I don't know. One of them has peanuts, though.

Woman: These are supposed to be half off. Ring them up and tell me how much they are.
Me: They're two dollars a piece, down from 5.
Woman: So they're not half off then.
Me: They're more than half off.
Woman: I don't want them then. Put them back.

Man: I've got a coupon for these things, but they're on sale too. Can I get both discounts?
Me: *examines coupons* No, because the value of the coupon would give you a negative total after the sale. I'll just use the coupon because you'll save more that way though.
Man: No, I came here for the sale price. Give me the coupon back. I'll use it some other time.

Me: Alright, your total is $2.25.
Man: *hands me a coupon for a free whatever-he-bought*
Me: *scans coupon, enters -2.25 in the register, giving him a $0.00 balance*
Man: That coupon says "maximum value $4.50" on it.
Me: Right, but the value of your purchase was only $2.25. That just means that had the stuff cost you $4.50, you could still get it for free, but it was cheaper than that.
Man: It SAYS maximum value $4.50!
Me: You're still getting it for free.
Man: THAT COUPON IS GOOD FOR $4.50!!!
Me: Yes, I know, but you only spent $2.25.
Man: I don't want it then. Put it all back and give me my coupon. This is bullshit.