Thank you. I had firgued out the session variables and was editing my original post before I saw your reply.
I also made it calculate tax based on ZIP code, but I hard coded it for CA tax. I'm sure there is a better way to do this, but this is my quick hack:
Code:
if($zipcode_estimate >= 90001 && $zipcode_estimate <= 96162){
$config["General"]["default_state"] = "CA";
}