diff --git a/addons/sale/tests/test_sale_order_down_payment.py b/addons/sale/tests/test_sale_order_down_payment.py
index e27d15e4028..ad7a641b095 100644
--- a/addons/sale/tests/test_sale_order_down_payment.py
+++ b/addons/sale/tests/test_sale_order_down_payment.py
@@ -811,3 +811,45 @@ class TestSaleOrderDownPayment(TestSaleCommon):
             [self.receivable_account.id, [],           5550.0,   0.0          ],
         ]
         self._assert_invoice_lines_values(invoice.line_ids, expected)
+
+    def test_so_with_multiple_line_rounding(self):
+        """Test downpayment fixed amount rounding when the sale order has
+           multiple lines that would create a sensible difference in rounding.
+        """
+        tax_20 = self.create_tax(20)
+
+        for i, price_unit in enumerate((10000, 10000, 10000, 50)):
+            self.sale_order.order_line[i].product_id = self.company_data['product_delivery_no'].id
+            self.sale_order.order_line[i].product_uom_qty = 1
+            self.sale_order.order_line[i].qty_delivered = 1
+            self.sale_order.order_line[i].tax_id = tax_20
+            self.sale_order.order_line[i].price_unit = price_unit
+
+        self.sale_order.order_line.qty_delivered_method = 'manual'
+        self.sale_order.action_confirm()
+
+        so_context = {
+            'active_model': 'sale.order',
+            'active_ids': [self.sale_order.id],
+            'active_id': self.sale_order.id,
+            'default_journal_id': self.company_data['default_journal_sale'].id,
+        }
+        payment_params = {
+            'advance_payment_method': 'fixed',
+            'fixed_amount': 840.0,  # with 20% tax applied, amount tax excluded is 700.0
+            'deposit_account_id': self.revenue_account.id,
+        }
+        downpayment = self.env['sale.advance.payment.inv'].with_context(so_context).create(payment_params)
+        action = downpayment.create_invoices()
+        invoice = self.env['account.move'].browse(action['res_id'])
+        expected = [
+            # keys
+            ['account_id',              'tax_ids',   'balance', 'price_total'],
+            # base lines
+            [self.revenue_account.id,    tax_20.ids, -700,      840.0],
+            # taxes
+            [self.tax_account.id,        [],         -140,      0.0],
+            # receivable
+            [self.receivable_account.id, [],         840.0,     0.0],
+        ]
+        self._assert_invoice_lines_values(invoice.line_ids, expected)
diff --git a/addons/sale/wizard/sale_make_invoice_advance.py b/addons/sale/wizard/sale_make_invoice_advance.py
index 46d4c211a5d..424f2098407 100644
--- a/addons/sale/wizard/sale_make_invoice_advance.py
+++ b/addons/sale/wizard/sale_make_invoice_advance.py
@@ -362,8 +362,11 @@ class SaleAdvancePaymentInv(models.TransientModel):
                 'product_uom_qty': 0.0,
                 'price_unit': 0.0,
             })
-            downpayment_line_map[grouping_key]['price_unit'] += \
-                order.currency_id.round(price_subtotal * percentage)
+            downpayment_line_map[grouping_key]['price_unit'] += price_subtotal
+        for key in downpayment_line_map:
+            downpayment_line_map[key]['price_unit'] = \
+                order.currency_id.round(downpayment_line_map[key]['price_unit'] * percentage)
+
 
         return list(downpayment_line_map.values())
 
diff --git a/addons/sale_project/tests/test_project_profitability.py b/addons/sale_project/tests/test_project_profitability.py
index d87ce6352ad..99881c616eb 100644
--- a/addons/sale_project/tests/test_project_profitability.py
+++ b/addons/sale_project/tests/test_project_profitability.py
@@ -593,7 +593,7 @@ class TestSaleProjectProfitability(TestProjectProfitabilityCommon, TestSaleCommo
         })
         # When a down payment is created, the default 15% tax is included. The SOL associated it then created by removing the taxed amount.
         # Therefore, the amount of the dp is higher than the amount of the sol created.
-        down_payment_invoiced = 100.01
+        down_payment_invoiced = 100.00
         downpayment.create_invoices()
         self.sale_order.invoice_ids[2].action_post()
         # Ensures the down payment is correctly computed for the project profitability.