I never have to think about calculating or filing tax, but I always see it and know exactly how much it is.
Of course most people have no idea how much VAT they pay for Amazon purchases in a year, but that's mostly a product of them not knowing how much they spend on Amazon in a year. If they know the latter, the former is trivial to figure out.
Due to complexity, all larger stores with multiple geographic locations would never have separate pricing signage for every single store, so they don't. Other stores do the same. It's all calculated at the register as things are scanned in the computer.
It may be weird for you when you visit, but, as we all grew up with it, it's just normal here.
Which is a long way of saying that even if you knew the total you spent at Amazon, you wouldn't be able to derive the total amount of sales tax paid.
FWIW, usually in the US it's just a line item on the receipt or checkout screen.
Wouldn't it be the opposite? Having a complicated tax system makes it harder to find out how much you're paying. If things were simpler it would be much more apparent.