I am storing shopping cart items in a multi-dimensional array that I assign to a session variable. During checkout, I have a page that reads the items in the cart and determines if they are allowed or not based on the state the user lives in. If they have an item that is not allowed, they can go back to the cart and remove the item. Once that item is removed, the checkout process resumes and is subjected to the same scan for items. If the user has removed the improper item, the page still shows they have it - but if you manually refresh the page, the item goes away and allows the user to continue.

How do I automatically refresh the page so the user doesn't have to?

You don't auto refresh the page, you prevent the browser from caching the page in the first place then it has to be requested again from the server and cart updates will be shown.
Add these lines to your ASP before you output any html:
Response.CacheControl = "no-cache"
Response.AddHeader "Pragma", "no-cache"
Response.Expires = -1

hth
Phil