My first thought is that while you should listen to your customer about no sales tax, be sure to confirm with the state that there is a no sales tax period. Don’t rely solely on the word of the customer. During the no sales tax period, you would need to turn off the collection of sales tax and that might require having Shopify walk you through it so that you don’t create a lot of work for yourself when you turn it back on.
When you file for periods in which sales taxes are not required, you typically will still file the total sales, non-taxable sales, and taxable sales. You can pull reports from Shopify that will give you those totals. Depending on how your accounting system is set up, your accounting team should be able to pull reports for these totals either within the accounting system or from Shopify.