--- a/cart.mjs
+++ b/cart.mjs
@@ -1,3 +1,7 @@
 export function total(items) {
-  return items.reduce((sum, x) => sum + x.price * x.quantity, 0);
+  const sum = items.reduce((sum, x) => {
+    if (!Number.isFinite(x.price) || !Number.isFinite(x.quantity) || x.price < 0 || x.quantity < 0) throw new RangeError("Invalid item");
+    return sum + x.price * x.quantity;
+  }, 0);
+  return Math.round((sum + Number.EPSILON) * 100) / 100;
 }