diff --git a/erpnext/controllers/taxes_and_totals.py b/erpnext/controllers/taxes_and_totals.py
index a4474b7780e..ee1fc632c06 100644
--- a/erpnext/controllers/taxes_and_totals.py
+++ b/erpnext/controllers/taxes_and_totals.py
@@ -32,11 +32,12 @@ from erpnext.utilities.regional import temporary_flag
 class calculate_taxes_and_totals:
 	def __init__(self, doc: Document):
 		self.doc = doc
-		frappe.flags.round_off_applicable_accounts = []
+		frappe.flags.round_off_applicable_accounts = (
+			get_round_off_applicable_accounts(self.doc.company, [], self.doc) or []
+		)
 		frappe.flags.round_row_wise_tax = frappe.get_single_value("Accounts Settings", "round_row_wise_tax")
 
 		self._items = self.filter_rows() if self.doc.doctype == "Quotation" else self.doc.get("items")
-		get_round_off_applicable_accounts(self.doc.company, frappe.flags.round_off_applicable_accounts)
 		self.calculate()
 
 	def filter_rows(self):
@@ -1240,14 +1241,16 @@ def get_itemised_tax_breakup_html(doc):
 
 
 @frappe.whitelist()
-def get_round_off_applicable_accounts(company, account_list):
+def get_round_off_applicable_accounts(
+	company: str, account_list: list | str, doc: str | dict | Document | None = None
+):
 	# required to set correct region
 	with temporary_flag("company", company):
-		return get_regional_round_off_accounts(company, account_list)
+		return get_regional_round_off_accounts(company, account_list, doc)
 
 
 @erpnext.allow_regional
-def get_regional_round_off_accounts(company, account_list):
+def get_regional_round_off_accounts(company, account_list, doc=None):
 	pass
 
 
diff --git a/erpnext/controllers/tests/test_taxes_and_totals.py b/erpnext/controllers/tests/test_taxes_and_totals.py
index 09d5231d7bc..54067c4ce22 100644
--- a/erpnext/controllers/tests/test_taxes_and_totals.py
+++ b/erpnext/controllers/tests/test_taxes_and_totals.py
@@ -1,3 +1,5 @@
+from unittest.mock import patch
+
 import frappe
 
 from erpnext.controllers.taxes_and_totals import calculate_taxes_and_totals
@@ -6,6 +8,28 @@ from erpnext.tests.utils import ERPNextTestSuite
 
 
 class TestTaxesAndTotals(ERPNextTestSuite):
+	def test_regional_round_off_accounts(self):
+		"""
+		Regional overrides cannot extend the list in-place — the return
+		value must be assigned back to frappe.flags.round_off_applicable_accounts.
+		"""
+		test_account = "_Test Round Off Account"
+
+		def mock_regional(company, account_list: list, doc=None) -> list:
+			# Simulates a regional override
+			account_list.extend([test_account])
+			return account_list
+
+		so = make_sales_order(do_not_save=True)
+
+		with patch(
+			"erpnext.controllers.taxes_and_totals.get_regional_round_off_accounts",
+			mock_regional,
+		):
+			calculate_taxes_and_totals(so)
+
+		self.assertIn(test_account, frappe.flags.round_off_applicable_accounts)
+
 	def test_disabling_rounded_total_resets_base_fields(self):
 		"""Disabling rounded total should also clear base rounded values."""
 		so = make_sales_order(do_not_save=True)
diff --git a/erpnext/public/js/controllers/taxes_and_totals.js b/erpnext/public/js/controllers/taxes_and_totals.js
index cb6c32a41b0..dc4f1e3bd61 100644
--- a/erpnext/public/js/controllers/taxes_and_totals.js
+++ b/erpnext/public/js/controllers/taxes_and_totals.js
@@ -231,6 +231,8 @@ erpnext.taxes_and_totals = class TaxesAndTotals extends erpnext.payments {
 				args: {
 					company: me.frm.doc.company,
 					account_list: frappe.flags.round_off_applicable_accounts,
+					// pass the doc so regional overrides can inspect it
+					doc: me.frm.doc,
 				},
 				callback(r) {
 					if (r.message) {