1. Make a copy of Order.php from:

/app/code/core/Mage/Sales/Model/Order.php

to:

/app/code/local/Mage/Sales/Model/Order.php

Then added the bold line below around line 1319:

$mailer->setTemplateParams(array(
'order' => $this,
'billing' => $this->getBillingAddress(),
'payment_html' => $paymentBlockHtml,
// Adds Grand Total to email
'total' => number_format($this->getGrandTotal(), 2)
)
);

The additional line will format the Grand Total to two decimal places. We were working on a single currency store, so we hard coded the currency symbol.

2. Add the ‘total’ variable to your Transactional¬†Email template:

£{{var total}}