Use "Other flows" tab to enter taxes.
There are 3 ways to enter amount of tax.
1. Enter Payment amount in the line of tax flow - "Payment Amnt" field.
2&3. Make a double click on the line of tax flow (1). Enter calculation base - Period, Int.calc.method, Base amount, Percentage Rate (2). Select either Percentage calculation or "Pro Rata Temporis / proportional to the time" (3). Calculated amount will be reflected in "Pmnt amount" field (4) and will be shifted to the line of tax flow by pressingbutton.