Flat rate 15% VAT/TAX added to all PMPro orders and checkouts

pmpro-flat-tax-rate-all-orders.php

<?php
/**
 * Add 15% tax to all PMPro checkouts.
 * Add this code to your site by visiting this guide - https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function customtax_pmpro_tax( $tax, $values, $order ) {
	$tax = round((float)$values['price'] * 0.15, 2);
	return $tax;
}
add_filter("pmpro_tax", "customtax_pmpro_tax", 10, 3);