Is there a way to disable sales tax calculation on SO sales orders?

You may think it a strange question.... but we use Avatax and we get dinged for each "transaction" hitting their server. Sales orders count as a transaction and each time we update orders (happens a lot) it counts as a transaction. There is no added value to us to have sales tax calculated on sales orders and we do not send sales orders to customers. Hence if we can turn off sales tax calculation we will be saving money.