On the dashboard page in your admin, click on Financial Stats, under the "General Stats" section. Set your date range, and then click on the "Export CSV" button. That will generate a csv file you can download from the Notifications > Generated Reports page. Open it in excel, and one of the line items on the spreadsheet will be "In-State Non-Taxable Sales".
How do I see how much I've sold in tax exempt product?
Using the financial report to see your non-taxable sales
Written by Paul Martin