How can I find sales numbers for Washington state excise taxes?

[detritusbooks]

In Washington (where I operate), we only pay excise taxes on sales that are shipped to customers in Washington. Unfortunately, I can't find the sales numbers for order that are shipped to Washington (so that I don't pay taxes for orders that get shipped outside of Washington), and Shopify UnHelp Center has no idea how to find this number. Anyone here know how to find this number?