Making change is a minor skill that probably should be taught in school. It actually doesn't involve any math, just counting, and that makes it more foolproof in a cashier type situation.
For those not familiar:
Say you have a bill totaling $3.08 and the customer hands you a $20.
"the total is" $3.08
(counting pennies)$3.09, $3.10
(counting nickels)$3.15
(counting dimes) $3.25
(counting quarters)$3.50, $3.75, $4.00
(counting dollars)"and one is" $5.00
(counting fives) "and five is" $10.00
(counting tens) "and ten is" $20.00
"There's your change sir/madam, have a good day."
That's the old fashioned way. And a good skill to have in a pinch, like if you are tending a simple cash box.
The issue is, people have become accustom to having the register display the change to tender. So nobody learns the "trick" of counting change, it's become irrelevant (sort of). However, when the system breaks down, they don't have a simple back-up, they have to use math and they get all panicky.