Audit Trail can tell you about events where a tag was assigned to an entry, but aside from that it doesn't really know which entries have a security tag.  You would need to run a report for each entry, which would be easiest by querying the audit view directly with a combined "where" clause.

And since you mention tagged folders, I should point out that folder tags don't inherit.  Documents in a tagged folder are not covered by that tag, and can be found in search results.