alt Hacker NewsThat's what frames are for. Only reload the frame with the important data in it (total cost, list of products in cart) and point the category links in the page to open in the same frame as the shopping cart. You can even style the frame contents with the main page's stylesheet so it only needs to load a `$41.29` total if that's all that's changed.
No, I did not defile myself that badly by using frames nor layout with tables either. <shudder> I did layout with CSS. It wasn't just an update to the total. It was a proper modern day UI look (if not so much feel) so that it had a collapsible shopping cart on the side so you could see the items and quantities and link back to the item's page.