I need to add way to drop the sales tax for non-profits

PRESSERO > *Pressero FAQs
You can advertise in your site that if a customer would like to order with tax exemption that they should contact you. They would provide the tax id so you can verify it, and then mark their account (or set them up with an account and mark it) with the status.
 
This way when they go to login next time they will not be charged tax. It is a common practice.