I Have Random Thoughts

We do it on the amount before the sales tax but I notice that in suggested tips printed on the receipts, they always do it on the amount including the sales tax.

I just tip the amount that's needed so I don't get any change back and don't have to give up my coins. :?
I know the US does it different, but I can't figure it out. It's too complicated for me :P

I base it on the final price, so whatever it is after tax.

I round up anyway ... so it doesn't make any difference to me