From the help menu:

To deactivate a tax rate:

Important! You will NOT be able to reactivate a tax rate. If you need it for future use, you’ll have to create a new one.

1. Select Taxes from the left menu.
2. In the Sales Tax Center, go to the Related Tasks section and select Add/edit tax rates and agencies.
3. Select a tax rate name then select Deactivate.
4. Select Continue on the dialog box.

there is no way to reactivate a sales tax rate.