This article will explain how to set up a tax exempt customer class in Counterpoint, so that customers in this class will not be charged tax if they have created an account on the site.
At the bottom of the form, under "Tax exempt tax codes", there are four input fields for selecting a tax code. You may select a "tax exempt" code in any of the 4 fields here.

Instructions on how to set up a Tax exempt tax code are outside the scope of this article - if you need help setting up such a code, your Counterpoint partner should be able to provide you with assistance.
If you sync up a tax exempt customer this way, note that the "Tax Exempt" group created will replace whatever other group the customer would have been in as defined by their Customer Category.