No, it has happened to me. More than once. I've been the dumb young cashier that snooty old dads pull this move on. Then they'd try to give me a patronizing math lesson, loudly, on the spot. Sometimes, their wives would at least grant me the dignity of looking embarrassed to be with them.
My own father has come home / over bitching about these exact same types of interactions too, over the years. Use your ******* credit card, if it bothers you so much DAD.
The thing is, I actually don't think most cashiers freeze up when they're given weird change because they are dumb. It's just unexpected, and they're often not sure why someone is giving them an odd configuration. Plus, there's usually a big line they're expected to keep moving. I think this kind of transaction should be alluded to in training, so that new workers will recognize it.
It only took being humiliated 3 or 4 times for me to be on the lookout for dad change tricks. Now, I'm not a cashier anymore, but I am an accountant lol. So definitely not too bad at math. And I'm old enough to have been taught math normally, anyway.
But yes, every subsequent generation is ruining the world, everyone younger than me is bad, etc.
EDIT: To clarify that I agree with Butter! and my comments here are towards the general issue, not to contradict Butter
This has a chance of making me pause, were I cashier, and I have a fricking degree in mathematics and an MBA.
The reason isn't "inability to perform basic arithmetic" so much as when a task is familiar enough to be routine, breaking that routine takes an extra moment, and also risks introducing human error. The whole reason to have a repetitive procedure is to enable a person to do a task multiple times, efficiently, with very few errors. It's not an abandonment of sentience, it's taking the repetitive task to a lower level in the brain so that conscious thought can be dedicated instead to paying attention to the customers, to noticing whether a bagger is coming by to help, if the customer has extra items in their cart, or any number of things more suited to a cashier's concentration than manual subtraction.
And yes--a different way of thinking and situational awareness can make it not at all a challenge to compute, but it has no chance of becoming routine unless it comes up often--and as noted, when it's not routine is when people make mistakes.
There honestly is a solution to that stays routine--if a customer hands you an excess, enter the total amount given anyway and have the register compute the change amount. If the customer's done it right and the cashier enters exactly what they're given, the result should be whole dollars as the customer desires. If the customer was just being absent-minded and gave more than they needed, or tried to make it round out and didn't get it quite right, they still get every penny they're due and the register stays balanced.
Being able to do simple math in your head is useful in life. While at a cash register I argue trying to use it in a transaction may be a detriment--at best, a basic estimate would be helpful as a "sanity check" on the register's output to make sure you didn't fat-finger a number or something.
I might also ask people more familiar with the job--if trying to get clever with the hand over of cash is exactly the point at which most scamming is attempted. If my guess on that is correct, it's another reason the cashier may become nervous and prefer to stick with procedure.