This module allows to add comision en voucher.

models/account_voucher.py

@@ -1,28 +1,27 @@
-# -*- coding: utf-8 -*-
-
 from openerp import models, fields, api
 
 
 class AccountVoucher(models.Model):
     _inherit = 'account.voucher'
 
-    comision = fields.Float(
+    comision = fields.Integer(
         string='Comisión',
         compute='_compute_comision',
         store=True
     )
 
-    @api.model
-    def _get_porcentaje(self):
+    @api.depends('amount')
+    def _compute_comision(self):
+
         param = self.env['ir.config_parameter'].get_param(
             'voucher_comision.porcentaje', '2'
         )
-        return float(param)
 
-    @api.depends('amount')
-    def _compute_comision(self):
-        porcentaje = self._get_porcentaje()
+        porcentaje = float(param)
 
         for rec in self:
-            rec.comision = rec.amount * porcentaje / 100 if rec.amount else 0
-
+            if rec.amount:
+                valor = rec.amount * porcentaje / 100
+                rec.comision = int(round(valor))
+            else:
+                rec.comision = 0

views/account_voucher_view.xml

@@ -24,7 +24,7 @@
             <field name="arch" type="xml">
 
                 <field name="amount" position="after">
-                    <field name="comision"/>
+                    <field name="comision" sum="Total Comisión"/>
                 </field>
 
             </field>