You need to get the entire hash contents at once if you want to sort them, so you can't use each.

use HTML::Entities qw( encode_entities );

for my $id (
    sort { $HASH{$a}{COUNT} <=> $HASH{$b}{COUNT} }
    keys(%HASH)
) {
    print "<tr>",
          "<td>", encode_entities($id),               "</td>",
          "<td>", encode_entities($HASH{$id}{COUNT}), "</td>",
          "</tr>\n";
}
[download]

I also fixed the bug where you were treating plain text as HTML.

Swap $a and $b if you want to sort in descending order.