Does TaxJar provide sales tax calculations for my Squarespace orders?

No. At this time we use our API to import your Squarespace transactions, which allows us to provide support for Sales Tax Reporting and Filing the sales tax you collect via Squarespace (if you choose to enroll in our AutoFile service), but the TaxJar API does not provide calculations for Squarespace orders. 

We have more details about our integration with Squarespace here.