As Decrease Amount setting not enabled for your calculation template it only increases ticket amount. If you need to always round by increasing ticket amount you can select Round Ticket Total Exactly setting as Calculation Method.
If you want to round nearest value (so it can increase or decrease depending on ticket amount) you’ll need two calculation types as explained at the beginning of this post. SambaPOS Rounding Features. In this case you’ll have two payment processors. One of them will work accordingly.