“I looked at the prices, and calculated all the stated prices in my head, plus the sales tax.”
Me too. Used to have the exact money and change in my hand ready for when the cashier would announce the total, then get a laugh at their expression.
Remember being sent out in 8th grade at lunchtime from school (with a couple of my mates and the money, no ther supervision) to walk to a local market and buy the supplies and carry them back for the home economics (how to cook) class in the school kitchen for that afternoon.