Try this:
global $post;
$tmp_post = $post;
//First get the list of terms
$terms = get_terms("post_tag");
//then loop over the list and get the posts of each term
echo "<ul>";
foreach ( $terms as $term ) {
$args = array('posts_per_page' => -1, 'tag' => $term->slug, 'post_type' => 'album');
$myposts = get_posts( $args );
if (count($myposts) > 0){
echo "<li>" .$term->name . "<ul>";
foreach( $myposts as $post ){
setup_postdata($post);
echo '<li><a href="'.the_permalink(); .'">'.the_title().'</a></li>';
}
echo "</ul></li>";
}
}
echo "</ul>";
$post = $tmp_post;