SPOD is not charging any Sales Tax for the time being, we will update these pages when we start charging Sales Tax.
We apply your sales tax rate based on the customers zip code. The tax rate is different in each state, and within each state, it varies by county, city, and district.
Usually sales tax is based on product + shipping cost, but there are exemptions.
Find more information on this question here: https://www.avalara.com/us/en/blog/2018/11/how-to-handle-sales-tax-on-shipping-a-state-by-state-guide.html