It's not recent that people don't know how to make change so the blame isn't fully on the use of computers instead of their heads. I remember back about 45 years ago before computerized registers that my supermarket used to have a lot of items for sale at 3 for $1. Cashiers had a problem if I bought only one item.
Another problem is that many young kids couldn't care less about getting the correct change, theirs included. It's the "whatever' attitude.