0.123499999996   rounds to 0.1235
    0.12345678999994 rounds to 0.12345679

##</code><code>##

if ($frac =~ /999.$/) {
    my ($zeroes, $digit) = $frac =~ /\.(.*)(.)$/;
    $digit = '0.' . 
        '0' x (length($zeroes)-1) .
        sprintf("%02d", 10 - $digit);
    $frac += $digit;
}