Unfortunately, you'll have to take County, State, and Zip Code out to get a total for the entire Region.
What I would do is create another view with these variables, and then make a Dual Axis map with the regions as you have them. On the Regions sheet, add the label.
Find example attached. You may have to tinker a little since I can't make a filed map with City or Zip with Superstore data, but you should be able to figure it out tinkering with that granularity.
Map Example.twbx 1.2 MB
This is a new functionality of Tableau 10 called "custom territory", see here:
Have also a look at this blog post I wrote, which is going to give you the option to swap between each territory overall sales and the detailed zip code sales.
Hope this helps,