This isn’t new. I’ve not had anyone count my change back to me in 25+ years, at least. The register tells the checkout person or cashier how much change you have coming, which is handed to you in a wad, and that’s it. I shudder to think of the scenes we’d have if the register DIDN’T do all the math for them.
Saying “Thank you” has gone the way of making change.
It’s arithmetic, not math.
When you deal in cash and paper, making change is quick and easy. You count back the change, starting with the price, up to the amount the customer handed you. My dad taught me when I was a kid, and I made change that way at a job for many years.
So, I, too, couldn’t understand why other cashiers had trouble when I could count change quickly in my head.
But, then... I took a retail job with a computer at the cash register. My old method of counting change didn’t work there. We had to input the amount the customer gave us. Then, the price would vanish, and only the change due would display. One busy day, a customer decided to change her amount of tender after I input it, and I had my own brain-freeze moment. Now, I will never judge another cashier again.