Tk::NumEntry supports -increment like so:

#!/usr/bin/perl
use strict;
use warnings;
use Tk 800;
use Tk::NumEntry;

my $mw = Tk::MainWindow->new( -title => 'Tk::NumEntry demo' );

my $ne = $mw->NumEntry(
  -value => 20.01,
  -increment => .2, 
)->pack();

# UPDATE: and you can always change the increment
# $ne->configure( -increment => .002 );

$mw->MainLoop();

1;
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