// 获取当前产品
$product = Mage::getModel('catalog/product')->load($productId);

// 获取税率计算器
$taxCalculator = Mage::getSingleton('tax/calculation');

// 获取税率请求对象
$request = $taxCalculator->getRateRequest(
    $shippingAddress, 
    $billingAddress, 
    $customerTaxClassId, 
    $storeId
);

// 获取产品税率
$taxRate = $taxCalculator->getRate($request->setProductClassId($product->getTaxClassId()));

echo "Tax rate for this product: " . $taxRate . "%";

$quote = Mage::getSingleton('checkout/session')->getQuote();
$taxAmount = $quote->getShippingAddress()->getTaxAmount();
$subtotal = $quote->getSubtotal();
$taxRate = ($taxAmount / $subtotal) * 100;

// 使用Magento的Ajax请求获取税率
function getProductTaxRate(productId, callback) {
    new Ajax.Request('/tax/calculation/getRate', {
        method: 'post',
        parameters: {
            product_class_id: productId,
            customer_class_id: Mage.Cookies.get('customer_class_id'),
            country_id: $('country_id') ? $('country_id').value : '',
            region_id: $('region_id') ? $('region_id').value : '',
            postcode: $('postcode') ? $('postcode').value : ''
        },
        onSuccess: function(transport) {
            var response = transport.responseText.evalJSON();
            callback(response.rate);
        }
    });
}