Tax rate Codes in Contract Billing

Hello,

I have a business requirement where I need to have a "specific" Geocode used on the Contract Billing line so that the applicable tax % is used . In this case   8.25%

Here is our current setup.

Job Master has blank Tax rate and Exp code fields

Customer AB record  in the job master has Geocode of  V140433390  with a   S  (EXP Code)     % = 9.0

Ship To AB record  (AN8) in the job  master has a Geocode of  V140310000   with a   S  (EXP Code)     % = 9.0

Contract Master has blank Tax rate and Exp code fields

Contract Billing Lines are set up with a V140890090  with a   S  (EXP Code)     % = 8.25 for this Unique Billing Scenario