How to handle "Restocking Fee"

If we create a negative percentage discount item for a restocking fee for a return authorization, it seems to work but it also discounts the tax. The tax amount should not be affected by this. Is there a way to not affect tax on the discount item or is it better to create a negative percentage markup and use it as a line item? What is best approach? The "Apply before sales tax" does not appear to have an affect either. It is currently unchecked and if the discount is selected from the dropdown, in my opinion it should not