I do this with cart & user pages.
To make sure its ssl, to pass PCI testing
<?php
// make sure its HTTPS
$uri = & JFactory::getURI();
$currentcheck=JURI::current();
$comparethis = str_replace( 'http:', 'https:', $currentcheck );
if ($comparethis !== $currentcheck){
$app = JFactory::getApplication();
$app->redirect($comparethis, null, null, true, true);
}
?>