Marketpress price including tax? How?

Alrighty, here's a new grenade for the discussion.

I'm using the marketpress shopping cart for physical goods. I am a reseller of jewelry from a Direct Sales company. The parent company actually charges us tax based on the suggested retail value for each piece when we buy it. They, then pay each state the sales taxes based on what we purchased.
Anyway.......

The taxes are now part of my cost. I found out the hard way that when a customer orders from out of state, they didn't pay the tax.

So, if I increase my cost per item to cover the tax, can I turn off the tax function for all states? I don't want those in my home state to pay tax on top of the price that already includes tax.

if so, do I just leave the tax amount blank?

Or, if I choose the price including tax, does that charge tax to every order regardless of state?