Reason #283,701 why I want to be a math teacher

I got my hair cut last week. As I was waiting in line to pay for the cut and some shampoo, the power went out. No problem for me, I was paying cash. Following is the sequence of events that occured as I stepped up to the register.

1) Cashier 1 writes up an invoice by hand that doesn't include tax on the shampoo, gives me the total.
2) Cashier 2 catches her mistake, but doesn't know what the sales tax rate is. Goes in the back to check.
3) Cashier 2 returns, and they huddle over the calculator together. Cashier 2 enters: $13.00 x 8.25. Yielding a sales tax of $107.25. Cashier 1: "That can't be right." I breathe a sigh of relief, because I wasn't carrying quite enough cash to cover an 825% sales tax rate.
4) Cashiers 1&2 stare at calculator.
5) I pipe up: "Enter thirteen times point-zero-eight-two-five." They look at me incredulously. "Trust me."
6) Cashier 2 enters 13 x zero-point-eight-two-five, yielding a sales tax of $10.725. She gives a befuddled little laugh that seems to say, "Where did my education go wrong?" Or maybe that's just how I interpreted it. Me: "thirteen times POINT-zero-eight-two-five".
7) Cashier 2 enters it correctly, yielding the much-more-budget-friendly sales tax amount of $1.0725. I'm glad they've got it, but wonder how they'll fare with the customers in back of me.
8) I restrain the urge to return the next day, math book in hand, and introduce these ladies to the lovely world of percentages. Instead, I file this story in the back of my head, to retrieve when my future students ask me, "But when are we ever going to USE this?" Every day folks, every single day.