Refactor: Move rounding to promotion calculator module

promotions/app/models/concerns/solidus_promotions/calculators/promotion_calculator.rb

@@ -6,6 +6,13 @@ module PromotionCalculator
       def description
         self.class.human_attribute_name(:description)
       end
+
+      private
+
+      def round_to_currency(number, currency)
+        currency_exponent = ::Money::Currency.find(currency).exponent
+        number.round(currency_exponent)
+      end
     end
   end
 end

promotions/app/models/solidus_promotions/calculators/percent.rb

@@ -10,9 +10,7 @@ class Percent < Spree::Calculator
       preference :percent, :decimal, default: 0
 
       def compute(object)
-        preferred_currency = object.order.currency
-        currency_exponent = ::Money::Currency.find(preferred_currency).exponent
-        (object.discountable_amount * preferred_percent / 100).round(currency_exponent)
+        round_to_currency(object.discountable_amount * preferred_percent / 100, object.order.currency)
       end
     end
   end

promotions/app/models/solidus_promotions/calculators/tiered_percent.rb

@@ -34,8 +34,7 @@ def compute_item(object)
         end
 
         if preferred_currency.casecmp(order.currency).zero?
-          currency_exponent = ::Money::Currency.find(preferred_currency).exponent
-          (object.amount * (percent || preferred_base_percent) / 100).round(currency_exponent)
+          round_to_currency(object.amount * (percent || preferred_base_percent) / 100, preferred_currency)
         else
           0
         end

promotions/app/models/solidus_promotions/calculators/tiered_percent_on_eligible_item_quantity.rb

@@ -23,8 +23,7 @@ def compute_line_item(line_item)
           eligible_line_items_quantity_total(order) >= value
         end
         if preferred_currency.casecmp(order.currency).zero?
-          currency_exponent = ::Money::Currency.find(preferred_currency).exponent
-          (line_item.discountable_amount * (percent || preferred_base_percent) / 100).round(currency_exponent)
+          round_to_currency(line_item.discountable_amount * (percent || preferred_base_percent) / 100, preferred_currency)
         else
           0
         end