[fix] Cur_frm breaking offline pos (#11955)

diff --git a/erpnext/public/js/controllers/taxes_and_totals.js b/erpnext/public/js/controllers/taxes_and_totals.js
index 1601ba2..6a08dbf 100644
--- a/erpnext/public/js/controllers/taxes_and_totals.js
+++ b/erpnext/public/js/controllers/taxes_and_totals.js
@@ -10,7 +10,7 @@
 				+ flt(item.price_list_rate) * ( flt(item.margin_rate_or_amount) / 100);
 		} else {
 			item.rate_with_margin = flt(item.price_list_rate) + flt(item.margin_rate_or_amount);
-			item.base_rate_with_margin = flt(item.rate_with_margin) * flt(cur_frm.doc.conversion_rate);
+			item.base_rate_with_margin = flt(item.rate_with_margin) * flt(this.frm.doc.conversion_rate);
 		}
 
 		item.rate = flt(item.rate_with_margin , precision("rate", item));