> Hmm, I argue that it's impossible, even in principle, to have a correct calculation of state sales tax due.
When you have conflicting interpretations just pick the one with the highest tax. If the customer disagrees they are always free to apply for a refund (and yes, States do have standard procedures and forms to apply for said refunds. Mistakes do happen.) If the customer is really going to leave over having to pay tax on their ball of yarn they probably aren't a customer that you want anyway.