> One solution could be to price things such that any amount of tax is included in the margin so the price is standard but profitability varies in minute ways between locations
Imagine you have customers in California (high taxes) and Wyoming (low taxes). You have one price, but the taxes in the former nets you zero profit. But, that's also where 98%+ of your customers are. That isn't going to work, needless to say.
The highest sales tax in California that I can find is 10.750% (lowest 7.50%). The highest in Wyoming is 6% (lowest 5%). That's not a wide spread. On many MANY items the existing profit margin is north of 30%, but even leaving that aside. Adding %10 to your base price to have a single price just means that in lower tax markets you're making more money. There's no obvious situation where you make less unless you intentionally under price your products and it eats into your margin.
Imagine you have customers in California (high taxes) and Wyoming (low taxes). You have one price, but the taxes in the former nets you zero profit. But, that's also where 98%+ of your customers are. That isn't going to work, needless to say.