I've got some information to share about completely removing the Tax line on your sales template in QuickBooks Online.
When setting up the sales tax in QBO, the tax line on the sales template will be visible. This way, you'll be able to enter the tax details in the said section. Being able to remove this line is currently unavailable. However, if you haven't set up the sales tax in the system, the tax line will not show up.
I can see how beneficial it would be for your business to have the tax line removed when no longer in need. I'll surely submit this preference to our developer so they can access this feedback and put it under consideration.
You can also visit our QuickBooks Online Blog site to be update with our latest news and updates including product enhancements.
I've also added here some links about customizing templates and on how sales tax works in QuickBooks Online: