Let me be the first to welcome you to the Community. I can help you remove the sales tax section in your invoices in QuickBooks Online.
You can create an invoice to show your patients balances without sales tax. Simply uncheck the Tax column in the transaction before sending it. See screenshots below:
If you wish to make a specific item non-taxable, edit the product/services and scroll down to Is taxable, then uncheck the box.
Here are some helpful articles for additional information:
That should get you pointed in the right direction. Post again in the Community if you need further assistance, I’m more than happy to help. Take care!