gistfile1.php

<?php
/**
 * WooCommerce Extra Feature
 * --------------------------
 *
 * Add custom fee to cart automatically
 *
 */
function woo_add_cart_fee()
{
    global $woocommerce;
    $woocommerce->cart->add_fee( __('Custom', 'woocommerce'), 5 );
}
add_action( 'woocommerce_cart_calculate_fees', 'woo_add_cart_fee' );