I'd imagine there's a module out there to do this, but I just threw this together in a couple of minutes. Besides, it was fun. :)

There are lots of times that I need to figure out this kind of stuff - I live on a boat and ride a motorcycle, so I'm always wrenching on something. In fact, I did something like this many, many years ago, but somehow managed to lose track of it... actually, I recall that implementation being quite a naive one (I was just starting to learn programming then.) Hope it's of use to others as well!

#!/usr/bin/perl
# By: Ben Okopnik <ben@okopnik.com>, 07:45 2012-07-16
# Finds nearest "tape measure" fraction for a given decimal
use warnings;
use strict;

die "Usage: ", $0 =~ /([^\/]+)$/, " <number> [tolerance]\n"
    unless @ARGV && $ARGV[0] =~ /^(\d+)?(\.\d+)$/;  # Yep, positives o
+nly :)
my $int = $1 || 0;
my $dec = $2;
die "No mantissa\n" unless $dec > 0;
die "Not a reasonable tolerance\n"
    if $ARGV[1] && $ARGV[1] !~ /^0?\.\d+$/;

my $tolerance = $ARGV[1] || .001;        # 1 mil is the default 
my $denom = 2;
{
    for my $num (1 .. $denom - 1){
        die $int + $dec, " is equal to $int $num/$denom (+/-$tolerance
+)\n"
            if abs($dec - $num / $denom) <= $tolerance;
    }
    $denom *= 2;
    redo;
}
[download]

-- 
I hate storms, but calms undermine my spirits.
 -- Bernard Moitessier, "The Long Way"