TaxCalcMode billing or shipping?
There is a known bug in ML8 when using TaxCalcMode = billing. Unless you have discovered otherwise from your state tax authorities, you should most likely be using TaxCalcMode = shipping anyway.
This varies from state to state, but tends to be shipping address unless the products are an electronically delivered product (e-books, e-documents, and electronically delivered software), which are usually considered to be shipped to your credit card billing address.
CHECK WITH YOUR STATE TAX AUTHORITIES
Erik Sutton
AspDotNetStorefront Technical Support