Cash payment details shown at the bottom of receipt is a reference for staff and customers to see amount that was paid in cash and change for customer. Do note that cash amount that is shown in the receipt does not include the tips, the amount shown is the actual amount of cash that was paid for the orders.
When customer pay by cash, go to Add payment > select Cash > choose the amount cash was given in options or specify the amount. If there is change for the bill, you may apply the change as tips or return the change to customer. If the change is tips, click Apply next to the pre-fill amount in the box. Then click Done and receipt will be printed. You may also print receipt on the order in Complete tab.
Note that the change amount will be 0 if the customer gives tips more than the Change due.