jenkins trigger build if new tag is released
Please note that the approach in the answer provided by stanjer doesn't make Jenkins trigger builds on new tags if they point to commits that were built before. For example, you tag release v1.0.0 (to make jenkins deploy this release), then on the future you have to rollback to v1.0.0, tagging its commit again, but with v1.0.0-rollback, Jenkins won't deploy your rollback because it will check the hash the tag points to, not the hash of the tag itself.
In summary, jenkins will only build new tags if they point to commits that are not tagged already, and this is currently not tweakable.
It would be awesome if one could use Jenkins as a CD tool working with tags for deploys and rollbacks.
More info here https://groups.google.com/forum/#!msg/jenkinsci-users/mYxtDNMz1ZI/xbX9-xM9BQAJ