Tax To One State

I've tried looking it up but nothing was clear for 4.3.8. I need to create a tax only for people whose billing address is in Idaho. All of our products have free shipping, so when they go to checkout, it doesn't add the 6%, and it just says no shipping required, even though I have the shipping method selected as "Use for free shipping"

Shipping methods and taxes are separate. Have a look at this.