Do you need more complex tax on your forms than just a flat rate? You can use custom pricing rules to modify the form total depending on the answers to questions.
You can setup a custom pricing rule to modify the total of the form by following these steps:
Note Custom pricing rules are applied in order so if two rules are in effect at the same time the lower one will affect rules above it.
You can also set a label to describe the custom pricing rule in the checkout.