In some countries or cities, certain guests are eligible for tax-exemption (e.g. government workers)
In order to do this, you need to create a Charge Type that doesn't have any taxes associated to it.
Go to [Settings] > [Accounting] > [Charge Types]
And create a new Charge Type that won't have any taxes associated to it. In this example, we will call it a "Tax Free Charge"
Make sure there's no tax checked to this charge type.
Now, when you create a new booking, you can select Tax Free Charge as Charge Type, and the nightly charges will not have taxes applied to it.