This is the sales tax and shipping tax specific version of the CalculationCodeCombine
This is the same as the DiscountCalculationCodeCombineMethodImplementation described above, except that the "Terminology" section should also have the following sentence:
Only one tax CalculationCode for each TaxType will be used for each OrderItem
. If more than one is "attached", only the "first" CalculationCode (according to its sequence attribute) is considered to be "attached".