Deploying multiple sites based on the same code and updating all

[eluser]Unknown[/eluser]
OK so I've built an ecommerce system in CI and its already been deployed a couple of times as a few different sites. With more sites in the pipeline I need to come up with a way of being able to implement updates across all the sites so that if a bug is found and fixed in one site, or if a new feature is added, then the changes to the models and controllers need to be updated across all the sites.

Is there a way to do this sort of thing in GIT or any other similar version control system?

Thx for any advice you can give.