Sales taxes and basic arithmetic

It's occurred to me a few times that perhaps one of the reasons kids today have problems with basic mathematical tasks is that they don't get the same kind of day-to-day mental math exercises that my generation did. <Geezer Voice>Back in my day, we didn't have sales taxes levied at the cash register, so even a five-year-old could figure out that a 10 cent candy bar and a 15 cent comic book could be paid for by that one quarter.</Geezer> Nowadays, it's a crapshoot for anyone under 12 to figure out if they have enough money to buy what they want (especially with weird things like the "no Provincial sales tax on prepared food under $4 except certain pre-prepared items, but there's still Gouge-and-Screw Tax".

I'm sure it's not the main reason for kids' mathematical weaknesses, but every time I have to wait for a young cashier to try to figure out correct change for me, I wonder.