Optional cash back amount to return to the customer.
For cash back transactions, the TransactionAmount must contain the sum total of the purchase amount PLUS the CashBack amount. If the purchase is for $10 and the customer requests $20 cash back, CashBack should be set to "20.00" and TransactionAmount must contain "30.00". This amount is to be specified in US dollars, without a dollar sign but with an explicit decimal point. For instance, ten dollars and fifty cents is to be specified as "10.50".
Note that only US currency is supported for debit and EBT cash benefit transactions.