Keep in mind that tax-exempt rules are not the same everywhere. In some places, not all types of products and services can be tax exempt. And sometimes, tax-exempt just means your customer only gets a certain percentage of tax discount.
If this seems a little complicated, don't worry. You just need to map your items to their proper tax categories, and make sure your customer's address is correct on each transaction. Then, QuickBooks follows the correct tax-exempt rules based on what you sell and your customer's address.