old_contents: from django.db import models
  from decimal import Decimal
  
  class CurrencyField(models.DecimalField):
      __metaclass__ = models.SubfieldBase
  
      def to_python(self, value):
          try:
              # TODO 5 may be correct for Switzerland. What about other countries?
              return super(CurrencyField, self).to_python(value).quantize(Decimal("0.05"))
          except AttributeError:
              return None
  
new_contents: from django.db import models
  from decimal import Decimal
  
  class CurrencyField(models.DecimalField):
      __metaclass__ = models.SubfieldBase
  
      def to_python(self, value):
          try:
              # TODO 5 may be correct for Switzerland. What about other countries?
              return super(CurrencyField, self).to_python(value).quantize(Decimal("0.05"))
          except AttributeError:
              return None
  
  try:
      from south.modelsinspector import add_introspection_rules
  
      CurrencyField_introspection_rule = ( (CurrencyField,), [], {}, )
  
      add_introspection_rules(rules=[CurrencyField_introspection_rule], patterns=["^zipfelchappe\.fields"])
  except ImportError:
      pass
subject: add south introspection rule