As you may already know, sales tax rates are different when the product you are selling is only made available via a download. All of our products in our Shopify store are downloadable only -- nothing is ever physically shipped to our customers.
We would love to have our sales tax be automatically determined by Shopify, but we're not sure if you are using the correct tax rates. Can you confirm that you are using tax rates that are specific to the type of product we are selling or is it the same for everything?
Shopify makes every effort to ensure that our automatic tax rates are as accurate as possible for merchandise sold within the United States. However, the onus is ultimately on you, the shop owner, to make sure that you are charging taxes appropriately to comply with local state tax laws.
You may want to reach out to an accountant or tax attorney here to ensure that our tax rates are appropriate for what you're selling, and if they do require reconfiguration for your download, you can always alter our automatic tax rates by switching over to manual taxation, as per this help doc: