Sales Tax Research Integrated into Navision

We are in the oil & gas industry and our business has grown in a way that we are doing business in multiple states. Since just about every state has different sales tax laws, it has become almost impossible to try to decipher the tax codes in determining correctly what is taxable vs. non-taxable in addition to the correct rates when we invoice our customers.

There are software programs that can be integrated into Navision that determine the taxable/non-taxable issue, but have too many required fields. The minimum required fields that I have found is city, zip and state. Since the bulk of our business is in the field (outside of incorporated jurisdictions), the required city field is not an option for us since we have to determine sales tax on the location where the actual work is performed.

Does anyone have any recommendations for sales tax software that can be integrated into Navision? It would be greatly appreciated.