query_posts exclude tags

Apologies if this has been asked and answered before. I have searched, but couldn’t find anything.

Is it possible to exclude tags in the query_posts() function? I tried using the same approach as with categories, resulting in either this:

query_posts(‘showposts=5&tag=-oldies’); // actually only shows ‘oldies’

or this:

query_posts(‘showposts=5&tag=-28’); //apparently the term_id or whatever

which doesn’t work at all.

Any ideas? Should I just use a combination of tags and categories to achieve the desired effect?