[% FOREACH item IN report.rows.values %]
   <tr>
     <td>[% item.id %]</td>
     <td>[% item.delta %] %</td>
   </tr>
[% END %]
##</code><code>##

#!/usr/bin/env perl 
use strict;
use warnings;
use Template;

my $r = {
    'rows' => { 
        'category1' => [
            {'id' => 'AAA', 'delta' => '0.01%'},
            {'id' => 'BBB', 'delta' => '0.03%'} ],
        'category2' => [ 
            {'id' => 'CCC', 'delta' => '0.02%'},
            {'id' => 'DDD', 'delta' => '0.04%'} ],
     },
};
my $text = q#
[% FOREACH item IN report.rows.values %]
   [% FOREACH one IN item %]
   <tr>
     <td>[% one.id %]</td>
     <td>[% one.delta %] %</td>
   </tr>
   [% END %]
[% END %]
#;

my $tt = Template->new;

$tt->process (\$text, {report => $r});