From 2c5c891a05438bc6ef499d5bdde63c16c285825d Mon Sep 17 00:00:00 2001
From: Alexander Lang <alex@cobot.me>
Date: Mon, 2 Feb 2026 16:21:03 +0100
Subject: [PATCH 1/2] fix rounding error caused by item quantity

when applying the line item quantity causes sub-cent amounts, the total needs to be rounded to 2 digits again.

fix https://github.com/halfbyte/ruby-secretariat/issues/46
---
 lib/secretariat/invoice.rb |  4 ++--
 test/invoice_test.rb       | 15 +++++++++++++++
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/lib/secretariat/invoice.rb b/lib/secretariat/invoice.rb
index 94826e3..140627b 100644
--- a/lib/secretariat/invoice.rb
+++ b/lib/secretariat/invoice.rb
@@ -121,12 +121,12 @@ def valid?
       @errors = []
       tax = BigDecimal(tax_amount)
       basis = BigDecimal(basis_amount)
-      summed_tax_amount = taxes.sum(&:tax_amount)
+      summed_tax_amount = taxes.sum(&:tax_amount).round(2)
       if tax != summed_tax_amount
         @errors << "Tax amount and summed tax amounts deviate: #{tax_amount} / #{summed_tax_amount}"
         return false
       end
-      summed_tax_base_amount = taxes.sum(&:base_amount)
+      summed_tax_base_amount = taxes.sum(&:base_amount).round(2)
       if basis != summed_tax_base_amount
         @errors << "Base amount and summed tax base amount deviate: #{basis} / #{summed_tax_base_amount}"
         return false
diff --git a/test/invoice_test.rb b/test/invoice_test.rb
index f6e1923..6ceaa6a 100644
--- a/test/invoice_test.rb
+++ b/test/invoice_test.rb
@@ -791,5 +791,20 @@ def test_invoice_object_extensions
       assert_match(/<ram:PaymentReference>#{invoice.payment_reference}<\/ram:PaymentReference>/, xml)
       assert_match(%r{<ram:DefinedTradeContact>\s*<ram:PersonName>Max Mustermann</ram:PersonName>\s*</ram:DefinedTradeContact>}, xml)
     end
+
+    def test_invoice_with_quantity_causing_sub_cent_amounts
+      invoice = make_de_invoice
+      invoice.tax_calculation_method = :ITEM_BASED
+      invoice.line_items.first.net_amount = BigDecimal('10.12')
+      invoice.line_items.first.billed_quantity = BigDecimal('0.1')
+      invoice.line_items.first.charge_amount = BigDecimal('1.01')
+      invoice.line_items.first.tax_amount = BigDecimal('0.19')
+      invoice.basis_amount = BigDecimal('1.01') # 1.012 rounded
+      invoice.tax_amount = BigDecimal('0.19')
+      invoice.grand_total_amount = BigDecimal('1.2')
+
+      invoice.valid?
+      assert_equal [], invoice.errors
+    end
   end
 end

From 855fae67192e474c0dc1dab7735022f841f05e61 Mon Sep 17 00:00:00 2001
From: Alexander Lang <alex@cobot.me>
Date: Mon, 2 Feb 2026 16:41:31 +0100
Subject: [PATCH 2/2] also apply rounding in line item

---
 lib/secretariat/line_item.rb |  2 +-
 test/invoice_test.rb         | 13 +++++++++++--
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/lib/secretariat/line_item.rb b/lib/secretariat/line_item.rb
index 9235fbb..4aea6b3 100644
--- a/lib/secretariat/line_item.rb
+++ b/lib/secretariat/line_item.rb
@@ -74,7 +74,7 @@ def valid?
       gross_price = BigDecimal(gross_amount)
       charge_price = BigDecimal(charge_amount)
       tax = BigDecimal(tax_amount)
-      unit_price = net_price * BigDecimal(billed_quantity.abs)
+      unit_price = (net_price * BigDecimal(billed_quantity.abs)).round(2)
 
       if charge_price != unit_price
         @errors << "charge price and gross price times quantity deviate: #{charge_price} / #{unit_price}"
diff --git a/test/invoice_test.rb b/test/invoice_test.rb
index 6ceaa6a..4e54ec1 100644
--- a/test/invoice_test.rb
+++ b/test/invoice_test.rb
@@ -793,9 +793,13 @@ def test_invoice_object_extensions
     end
 
     def test_invoice_with_quantity_causing_sub_cent_amounts
+      errors = []
+
       invoice = make_de_invoice
       invoice.tax_calculation_method = :ITEM_BASED
       invoice.line_items.first.net_amount = BigDecimal('10.12')
+      invoice.line_items.first.gross_amount = BigDecimal('10.12')
+      invoice.line_items.first.discount_amount = BigDecimal('0')
       invoice.line_items.first.billed_quantity = BigDecimal('0.1')
       invoice.line_items.first.charge_amount = BigDecimal('1.01')
       invoice.line_items.first.tax_amount = BigDecimal('0.19')
@@ -803,8 +807,13 @@ def test_invoice_with_quantity_causing_sub_cent_amounts
       invoice.tax_amount = BigDecimal('0.19')
       invoice.grand_total_amount = BigDecimal('1.2')
 
-      invoice.valid?
-      assert_equal [], invoice.errors
+      begin
+        invoice.to_xml(version: 2)
+      rescue ValidationError => e
+        errors = e.errors
+        pp e.errors
+      end
+      assert_equal [], errors
     end
   end
 end