Add tax subtext to Fees line similar to Subtotal and Shipping lines

wc-add-tax-subtext-fees.php

/**
 * Add tax subtext to Fees line
 * Code snippets should be added to the functions.php file of your child theme
 *
 * @return string
 */
add_filter( 'woocommerce_cart_totals_fee_html', 'add_tax_subtext_on_fees', 10, 2 );
function add_tax_subtext_on_fees( $cart_totals_fee_html, $fee ) {

	if( $fee->taxable ) {
	    if ( WC()->cart->display_prices_including_tax() ) {
			if ( $fee->tax > 0 && ! wc_prices_include_tax() ) {
				$cart_totals_fee_html .= ' <small class="tax_label">' . WC()->countries->inc_tax_or_vat() . '</small>';
			}
		} else {
			if ( $fee->tax > 0 && wc_prices_include_tax() ) {
				$cart_totals_fee_html .= ' <small class="tax_label">' . WC()->countries->ex_tax_or_vat() . '</small>';
			}
		}
	}

	return $cart_totals_fee_html;
}