I just set up my TaxJar account and am using the free trail after reading this forum. TaxJar integrates with SquareSpace in terms of calculating the sales tax you need to pay and appears pretty seamless. So at least you'll be compliant on the sales tax payment, just not always charging the correct amount of sales tax at checkout from the customer. Looks like TaxJar's transaction reporting and analytics could potentially warn you if you were charging too much or too little though. I think SquareSpace is still a great site to use for selling and shipping physical products in "origin-based" states like California that we are based in.