Right now, there's a huge number of elected people in the US who wield real local power through these taxes and other rules that they can make.
It's a headache but we live in the computer age and we can automate administrative things like tax calculation at checkout; we should be using systems to aid decentralization and democratization instead of the opposite.
If I’m buying online with a digital transaction you can charge whatever cents are necessary.
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.