Ajaxify your cart viewer so it updates when an item is added (via ajax)
// Ensure cart contents update when products are added to the cart via AJAX (place the following in functions.php)
add_filter('add_to_cart_fragments', 'woocommerce_header_add_to_cart_fragment');
function woocommerce_header_add_to_cart_fragment( $fragments ) {
global $woocommerce;
ob_start();
?>
<a class="cart-contents" href="<?php echo $woocommerce->cart->get_cart_url(); ?>" title="<?php _e('View your shopping cart', 'woothemes'); ?>"><?php echo sprintf(_n('%d item', '%d items', $woocommerce->cart->cart_contents_count, 'woothemes'), $woocommerce->cart->cart_contents_count);?> - <?php echo $woocommerce->cart->get_cart_total(); ?></a>
<?php
$fragments['a.cart-contents'] = ob_get_clean();
return $fragments;
}