Knowing the sales tax at a particular in-person store is more feasible, and that’s the only case where you have to deal with cash.

If I’m buying online with a digital transaction you can charge whatever cents are necessary.

You then still have the issue of standardized advertising prices.

Right now, a company can say they sell gadget X for $999, which would not be possible if they had to work out item taxes.

The other possibility is that they now have to mark X up to take into account the most pessimistic possible tax rate and advertise the marked-up rate.