It shouldn't be needed to change the strategy to use a diffferent price object when OSCAR_OFFERS_INCL_TAX setting is changed

src/oscar/apps/partner/prices.py

 from oscar.core import prices
+from django.conf import settings
 
 
 class Base(object):
     #: Price to use for offer calculations
     @property
     def effective_price(self):
+        if settings.OSCAR_OFFERS_INCL_TAX:
+            return self.incl_tax
         # Default to using the price excluding tax for calculations
         return self.excl_tax