I'm surprised it's not mentioned on other comments, but in Japan, the whole thing is automated. The cashier feeds the cash notes / coins into a machine, and the machine spits out the exact change. It's super-fast, even when the cashier counts your change in front of your eyes, and lays it out neatly onto a tray[0].

I wonder how come these types of machines aren't more popular in other countries.

[0] sounds like some super fancy concierge service, but it's pretty much standard, from 7-eleven to fancy stores