GACO: custom fee

function woo_dm_add_custom_fees(){
    $cart_total = 0;
    foreach( WC()->cart->get_cart() as $item ){
        $cart_total += $item["line_total"];
    }
    $fee = (int)$cart_total*5/100;
    WC()->cart->add_fee( "Credits :", $fee, false, '' );
}

add_action( 'woocommerce_cart_calculate_fees' , 'woo_dm_add_custom_fees' );
add_action( 'woocommerce_after_cart_item_quantity_update', 'woo_dm_add_custom_fees' );