This plugin ties Shopp, a WordPress e-commerce plugin, into Washington State's Department of Revenue API to lookup destination-based sales tax and calculate it on the fly.
Trusted by more than 20,000 businesses, TaxJar’s award-winning solution makes it easy to automate sales tax reporting and filing, and determine economic nexus with a single click.
Avior SutTax offers sales tax determination web service to retailers. With SutTax WooCommerce Plugin, retailers are able to add accurate sales tax to their invoices.