better tax aggregation

app/helpers/checkout_helper.rb

@@ -54,12 +54,9 @@ module CheckoutHelper
   end
 
   def display_adjustment_tax_rates(adjustment)
-    tax_rate = (adjustment.included_tax / (adjustment.amount - adjustment.included_tax)).round(2)
-    if tax_rate == 0 || tax_rate.infinite?
-      ""
-    else
-      number_to_percentage(tax_rate * 100, :precision => 1)
-    end
+    tax_rates = adjustment.tax_rates
+    return "" if adjustment.amount == adjustment.included_tax
+    tax_rates.map { |tr| number_to_percentage(tr.amount * 100, :precision => 1) }.join(", ")
   end
 
   def display_adjustment_amount(adjustment)

app/models/spree/adjustment_decorator.rb

@@ -34,10 +34,30 @@ module Spree
       included_tax > 0
     end
 
-    def display_included_tax
-      Spree::Money.new(included_tax, { :currency => currency })
+    def tax_rates
+      case originator
+      when Spree::TaxRate
+        [originator]
+      when EnterpriseFee
+        case source
+        when Spree::LineItem
+          tax_category = originator.inherits_tax_category? ? source.product.tax_category : originator.tax_category
+          return tax_category ? tax_category.tax_rates.match(source.order) : []
+        when Spree::Order
+          return originator.tax_category ? originator.tax_category.tax_rates.match(source) : []
+        end
+      else
+        [find_closest_tax_rate_from_included_tax]
+      end
     end
 
+    def find_closest_tax_rate_from_included_tax
+      approximation = (included_tax / (amount - included_tax))
+      return nil if approximation.infinite? or approximation.zero?
+      Spree::TaxRate.order("ABS(amount - #{approximation})").first
+    end
+
+
     def self.without_callbacks
       skip_callback :save, :after, :update_adjustable
       skip_callback :destroy, :after, :update_adjustable

app/models/spree/order_decorator.rb

@@ -234,12 +234,12 @@ Spree::Order.class_eval do
 
   def tax_adjustment_totals
     tax_adjustments.each_with_object(Hash.new) do |adjustment, hash|
-      if adjustment.originator_type == "Spree::TaxRate"
-        tax_rate = adjustment.originator.amount
-      else
-        tax_rate = (adjustment.included_tax / (adjustment.amount - adjustment.included_tax)).round(2)
-      end
-      hash.update({tax_rate => adjustment.included_tax}) { |_tax_rate, amount1, amount2| amount1 + amount2 }
+      tax_rates = adjustment.tax_rates
+      tax_rates_hash = Hash[tax_rates.collect do |tax_rate|
+        tax_amount = tax_rates.one? ? adjustment.included_tax : tax_rate.compute_tax(adjustment.amount)
+        [tax_rate.amount, tax_amount]
+      end]
+      hash.update(tax_rates_hash) { |_tax_rate, amount1, amount2| amount1 + amount2 }
     end
   end
 

lib/open_food_network/enterprise_fee_applicator.rb

@@ -32,21 +32,11 @@ module OpenFoodNetwork
     end
 
     def adjustment_tax(adjustable, adjustment)
-      tax_rates = rates_for(adjustable)
+      tax_rates = adjustment.tax_rates
 
       tax_rates.select(&:included_in_price).sum do |rate|
         rate.compute_tax adjustment.amount
       end
     end
-
-    def rates_for(adjustable)
-      case adjustable
-      when Spree::LineItem
-        tax_category = enterprise_fee.inherits_tax_category? ? adjustable.product.tax_category : enterprise_fee.tax_category
-        return tax_category ? tax_category.tax_rates.match(adjustable.order) : []
-      when Spree::Order
-        return enterprise_fee.tax_category ? enterprise_fee.tax_category.tax_rates.match(adjustable) : []
-      end
-    end
   end
 end