I don't know what they teach children in school. Without a calculator most high school grads can't make change.
I've tripped up quite a few young cashiers. Say the bill is $13.20, I hand them $15 (ten bill and a five bill) plus a quarter coin. If they can't punch in $15.25 as amount tendered to automatically get the change amount shown, they get confused. When my daughters were young kids (who knew how to do math in their heads), they would snicker at the confused cashier.
I drilled math into their heads. Say you want to buy 3 dolls, each $1.98, how much is that before tax? They'd multiply 3 x $2, then subtract 3 x 2 cents, or in other words $6 minus 6 cents getting $5.94. Math taught this way is fun. The commie teachers in schools now, are humorless drones that haven't the best interests of their students in mind.