function post_type_tags_fix($request) {
if ( isset($request['tag']) && !isset($request['post_type']) )
$request['post_type'] = 'any';
return $request;
}
add_filter('request', 'post_type_tags_fix');
You can alter the post type to your liking.
From this post.
Custom post type tag archives don’t work for basic loop?