Tip portion of the TransactionAmount .
This property is only applicable to Restaurant (table service) transactions. It may contain up to 8 characters in the format "DDDDD.CC", left-justified with no fill. (eg "1.99").
Note that the TransactionAmount should always include any GratuityAmount. For example, if the sale price of the transaction is $10.00, and the tip on the transaction is $3.00 (for a grand total of $13.00), the TransactionAmount property should contain "13.00" and the GratuityAmount property should contain "3.00".