During Magento One Page Checkout, We used to display order details (subtotal, tax, shipping, grand total ) at Payment Information section. Use checkout session, to retrieve order data. Check below code for reference.
//Order Totals
$orderDetails = Mage::getSingleton('checkout/session')->getQuote()->getTotals(); //Total object
$subtotal = $orderDetails["subtotal"]->getValue(); //Subtotal value
$shippingAmount = Mage::getSingleton('checkout/session')->getQuote()->getShippingAddress()->getShippingAmount();
//Shipping Amount
$taxAmount = Mage::helper('checkout')->getQuote()->getShippingAddress()->getData('tax_amount') //Tax Amount if(isset($orderDetails['discount']) && $orderDetails['discount']->getValue()) {
$discount = $orderDetails['discount']->getValue(); //Discount value if applied
}
$grandtotal = $orderDetails["grand_total"]->getValue(); //Grand Total