Write a tax rule to make all Gov't classified customers as tax exempt.

Need a solution for client where 50% of their customer base are Gov't agencies who are non-taxable.  Is there a way to classify customers as 'GOVERNMENT' and write a tax rule where all customers that are classified as GOVERNMENT are non-taxable.  Client would prefer this as opposed to having to flag each customer ship-to site as exempt.  Any suggestions would be appreciated.