<?php
$order = $this->getOrder();
$shippingTaxClassId = Mage::getStoreConfig('tax/classes/shipping_tax_class',$order->getStoreId());
$customerGroupId = $order->getCustomerGroupId();
$group = Mage::getModel('customer/group')->load($customerGroupId);
$custTaxClassId = $group->getTaxClassId();
$store = Mage::getModel('core/store')->load($order->getStoreId());
$taxCalculationModel = Mage::getSingleton('tax/calculation');
$request = $taxCalculationModel->getRateRequest($order->getShippingAddress(), $order->getBillingAddress(), $custTaxClassId, $store);
$shippingTaxPercent = $taxCalculationModel->getRate($request->setProductClassId($shippingTaxClassId));
?>