Earlier quoted context omitted.
No they cannot. Taxes are not uniform. Walmart probably won't deal with this, but in many states business (read farmers) do not pay sales tax on some items (read likely to be used on a farm) and so stores that want to sell to business will have the ability to verify you are a business to give that discount. It is worse for online where until you log in they have no clue what taxes will apply. If you are buying a gift…
If you sell a widget in a store, you MUST be able to compute the sales tax. Otherwise, you can't sell it. And if you can do that, then you might as well print it on the price tag (along with pre-tax price if you want). No buts. Ditto for online, after you get the customer's ZIP code.
Fun fact: sales tax rates are not stable. Our state publishes quarterly tax changes at the county level; city-level changes are presumably too numerous for the state to publish in the same format.
Inclusive pricing can obviously be done in-store, but it also more or less ensures that some of the items in your store will have incorrect prices some of the time.