#! /usr/bin/perl

use strict;
use warnings;

my %h;

# if your data is really numerical then the apostrophes are superfluous
$h{10}{20} = 5;
$h{10}{25} = 4;
$h{05}{50} = 3;
$h{20}{30} = 2;

my @temp;

for my $key1 ( keys %h ) {
  for my $key2 ( keys %{ $h{$key1} } ) {
    # create a 3-column table from your hash
    push @temp, [ $key1, $key2, $h{$key1}{$key2} ];
  }
}

# sort it by the second column numerically
for ( sort { $a->[1] <=> $b->[1] } @temp ) {
  print 'key1=', $_->[0], ', key2=', $_->[1], ', value=', $_->[2], "\n";
}