Why don't they expect sales tax?

"How much is this cutter, Cosgriff?" he asked.

"$40".

"Okay, I'll take it."

"Thanks. That'll be $42.40".

"What?" he asks in shock. "You just told me it was forty dollars!"

You haven't heard of sales tax, buddy? But we get that reaction all the time when making an over the counter sale. Whether you like sales taxes or not, why wouldn't you expect me to charge it? Do you ask the cashier at Kroger the same things when she rings you up? Why do you ask me?

Apparently some customers believe that our store is in some time warped part of Michigan where the state sales tax doesn't apply. To this day it amazes me when guys express dismay at my collecting it. I don't get it. If you have a rational explanation for that, I'd love to hear it.