Hugo,
Looks like your really getting into SambaPOS
There is no easy way to apply a $ discount to the ticket total, besides changing price on an item using the Change Price button.
Since we cannot make calculations like this using Rules & Actions, we can use Printer Templates instead.
1. Create a Printer Template 'Discount Rates' and use the following lines in the Footer
<T>Discount Ticket
<F>-
<J01>Total|${TICKET TOTAL}
<F>-
<J00>Discount Amount|Discount %
<F>-
<J00>$5|[=Format(5 / ToNumber('{TICKET TOTAL}') * 100)]%
<J00>$10|[=Format(10 / ToNumber('{TICKET TOTAL}') * 100)]%
<J00>$15|[=Format(15 / ToNumber('{TICKET TOTAL}') * 100)]%
<J00>$20|[=Format(20 / ToNumber('{TICKET TOTAL}') * 100)]%
<F>-
2. Create Print Job 'Discount Rates'
Button - 'Discount Rates'
Tick only - Display at POS & Display at Payment
Printing Content - All Lines
Auto Print - Manual
Map to your Receipt Printer using Discount Rates template
3. Add Discount Rates print job to your Terminal (Settings->Terminals)
4. Now you have a 'Discount Rates' button on your screen that will print a Discount Rates ticket like below
Discount Ticket
--------------------------------------------
Total $82.00
--------------------------------------------
Discount Amount Discount %
--------------------------------------------
$5 6.10%
$10 12.20%
$15 18.29%
$20 24.39%
--------------------------------------------
Hope this helps.
FYI - SambaPOS V3 can do calculations using Rules & Actions
