Shopping Cart show text if Total Shipping cost is zero

This changes the Total Shipping item in the shopping cart using existing filters so can go in the themes functions.php file:

//cart shipping price filter
// filters "Total Shipping" amount in cart
function cart_shipping_to_be_determined(){
	global $wpsc_cart;
	$result=($wpsc_cart ->calculate_total_shipping());
	if(!$result > 0){
		$result ="To be determined";
		return $result;
	}
	return $result;
}

add_filter('wpsc_cart_shipping', 'cart_shipping_to_be_determined');