AbleCommerce Shopping Cart Software

Is there any way to bypass Sales Tax Calculations when calling ? I'm creating a new Sales Tax Provider for TaxJar. They charge per "transaction". They include API usage as a transaction. Unfortunately, it fires on the basket, and at each stage of the checkout. I only want it to fire on the final stage of checkout after the billing, shipping, and ship method have been selected.

The only alternative I can think of is to look at the source for and create a helper or extension method that performs everything except the tax calculations. Your thoughts?