Explain the reason for evtl. tax mismatch.

document.py

@@ -101,12 +101,15 @@ class Incoming(metaclass=PoolMeta):
             UserError: if calculated values dont match
                 with xml-values
         """
+        pool = Pool()
+        Configuration = pool.get('account.configuration.tax_rounding')
+        configuration = Configuration(1)
+
         totals = self.parsed_data.get('total', None)
         if not totals:
             raise UserError(gettext(
                 'msg_convert_error.msg_convert_error',
                 msg='no totals-section in xml-data'))
-
         for xfield, inv_field in [
                 ('taxbase', 'untaxed_amount'),
                 ('taxtotal', 'tax_amount'),
@@ -115,15 +118,25 @@ class Incoming(metaclass=PoolMeta):
             inv_val = getattr(invoice, inv_field)
 
             if xml_val != inv_val:
-                raise UserError(gettext(
-                    'document_incoming_invoice_xml.msg_convert_error',
-                    msg=' '.join([
+                rounding = configuration.tax_rounding
+                field_name = 'tax_rounding'
+                selection_values = configuration.fields_get(
+                    [field_name])[field_name]['selection']
+                rounding_cfg = [
+                    i[1] for i in selection_values if i[0] == rounding][0]
+                msg = ' '.join([
                         inv_field + ' mismatch',
                         'from-xml=' + Report.format_currency(
                             xml_val, None, invoice.currency),
                         'calculated=' + Report.format_currency(
                             inv_val, None, invoice.currency)
-                    ])))
+                        ])
+                msg += '\n\n' + gettext(
+                    'document_incoming_invoice_xml.msg_tax_amount_mismatch',
+                    rounding=rounding_cfg)
+                raise UserError(gettext(
+                    'document_incoming_invoice_xml.msg_convert_error',
+                    msg=msg))
 
     def _readxml_xpath(self, tags):
         """ generate xpath

locale/de.po

@@ -46,6 +46,9 @@ msgctxt "model:ir.message,text:msg_unused_linevalues"
 msgid "The following data was not used to generate the invoice line:"
 msgstr "Die folgenden Daten wurden für die Erzeugung der Rechnungszeile nicht verwendet:"
 
+msgctxt "model:ir.message,text:msg_tax_amount_mismatch"
+msgid "You have configured tax rounding method '%(rounding)s' in the account configuration. Maybe try with a different method"
+msgstr "In Rechnungswesen/Einstellungen ist die Steuerrundungsmethode '%(rounding)s' eingetragen. Versuchen Sie es u.U. mit einer anderen Methode'
 
 ###################################
 # document.incoming.configuration #

message.xml

@@ -35,6 +35,9 @@
         <record model="ir.message" id="msg_unused_linevalues">
             <field name="text">The following data was not used to generate the invoice line:</field>
         </record>
+        <record model="ir.message" id="msg_tax_amount_mismatch">
+            <field name="text">You have configured tax rounding method '%(rounding)s' in the account configuration. Maybe try with a different method</field>
+        </record>
 
     </data>
 </tryton>