Required for the lowest rate on Commercial/Purchasing card (Level 2) transactions.
This property may be up to 9 characters, in the format "DDDDDD.CC", and be left-justified with no fill. (eg: "1.99"). Note that the TaxAmount should be included in the total TransactionAmount. For example, if the sale price of the transaction is $10.00, and the tax on the transaction is $0.60 (for a grand total of $10.60), the TransactionAmount property should contain "10.60" and the TaxAmount property should contain "0.60".