How Much Longer?

I was at the store yesterday and watched a cashier who was stymied by a customer paying cash. She is so used to people paying electronically that she was unsure how to make change. She even had problems getting the cash out of the mmf drawer. I wonder how much longer it will be before businesses stop taking cash altogether. Credit cards, debit cards and online transactions are taking over, it's only a matter of time before cash is passe.