printf("%.­5f\n", sprintf("%­.6f1", $_))

##</code><code>##

printf( "%.5f\n", sprintf("%.12e",$_) )
#                            ^^^

##</code><code>##

 % perl -le "print 0.00003499999999999999"
3.5e-05

##</code><code>##

my %c;
for my $i (  '00' .. '99'  ) {
    my $f= 0 + ".${i}5";
    my $r= sprintf "%.2f", $f;
    my $d= $r < $f ? '-' : '+';
    $c{$d}++;
    print "$f $r $d\n";
}
print "$c{'-'} rounded down, $c{'+'} rounded up.\n";
__END__
0.005 0.01 +
0.015 0.01 -
0.025 0.03 +
0.035 0.04 +
0.045 0.04 -
0.055 0.06 +
...
0.905 0.91 +
0.915 0.92 +
0.925 0.93 +
0.935 0.94 +
0.945 0.94 -
0.955 0.95 -
0.965 0.96 -
0.975 0.97 -
0.985 0.98 -
0.995 0.99 -
50 rounded down, 50 rounded up.