magento update Total Paid after payment - magento

Question

I have my own custom payment gateway which is working ok with one problem. When a transaction is successful the order gets updated and the email sent but the Total paid is still €0.
How do I update the paid status? I cannot find any articles on this.
Magento 1.7
public function responseAction() {
if($this->getRequest()->isPost()) {
if($payment_validated) {
// Payment was successful, so update the order's state, send order email and move to the success page
$order = Mage::getModel('sales/order');
$order->loadByIncrementId($orderId);
$order->setState(Mage_Sales_Model_Order::STATE_PROCESSING, true, 'AIB has authorized the payment.');
$order->sendNewOrderEmail();
$order->setEmailSent(true);
$order->save();
Mage::getSingleton('checkout/session')->unsQuoteId();
Mage_Core_Controller_Varien_Action::_redirect('checkout/onepage/success', array('_secure'=>true));
}

Answer 1

This answer might be little out of date but still someone might find it helpful.
I myself found this question and wanted an answer for this one.
So i found a very helpful article at atwix and specifically I used:
$orderId = 200000025; // you'll get your own Order Id
$model = Mage::getModel('sales/order');
$model->loadByIncrementId($orderId);
$invoice = $model->prepareInvoice();
$invoice->register();
Mage::getModel('core/resource_transaction')
->addObject($invoice)
->addObject($invoice->getOrder())
->save();
$invoice->sendEmail(true, '');
if($model->setState(Mage_Sales_Model_Order::STATE_PROCESSING, true)) {
$model->save();
}
So after this I got payment status to Paid in the backend and also changed the status to processing.
Now next step is to let customer know that he's order has been paid and I would like to do it via email.
Cheers!!