diff --git a/shop/price.go b/shop/price.go
index 279dea1..d2eba10 100644
--- a/shop/price.go
+++ b/shop/price.go
@@ -1,3 +1,6 @@
+// Package shop prices orders.
+//
+// Extra lines shift every function down.
 package shop
 
 // Discount returns the price after applying a percentage discount.
@@ -26,3 +29,11 @@ func Clamp(v, lo, hi int) int {
 	}
 	return v
 }
+
+// Tax returns VAT on an amount.
+func Tax(amount int) int {
+	if amount <= 0 {
+		return 0
+	}
+	return amount / 5
+}
diff --git a/shop/price_test.go b/shop/price_test.go
index ed08fbd..fede788 100644
--- a/shop/price_test.go
+++ b/shop/price_test.go
@@ -22,3 +22,9 @@ func TestClamp(t *testing.T) {
 		t.Fatal("in range")
 	}
 }
+
+func TestTax(t *testing.T) {
+	if Tax(100) != 20 {
+		t.Fatal("tax")
+	}
+}