Dynamics NAV - LS Retail - POS Design - Create a button that inserts a specific amount for a tender type

Problem:
We have a situation where we want users to be able to collect payments in only 100 or 500 amounts, and want to force two specific buttons that enter a fixed payment amount.

Solution:
On the button, if you have it enter the amount first, and then run the tender type, it accepts the payment.

Command: amount_k
Parameter: 100 (payment amount)
Post command: tender_k
Post Parameter:20 (tender type)