The @{[...]} trick is useful for interpolating the result of a chunk of code into a string.

No doubt a nice trick... but in this particular case, the conversion to string would happen implicitly, i.e. you could also do

    ($o *= $e) =~ /(0\.0*\d{0,5})/;
[download]

Yet another way would be to use bignum's accuracy option (which also does take care of the rounding)

use bignum accuracy => 5;

my $e = 0.00141;
my $o = 1;
for (1 .. 10) {
    $o *= $e;
    print "$o\n";
}
__END__
0.0014100
0.0000019881
0.0000000028032
0.0000000000039525
0.0000000000000055730
0.0000000000000000078579
0.000000000000000000011080
0.000000000000000000000015623
0.000000000000000000000000022028
0.000000000000000000000000000031059
[download]

(see Math::BigInt and Math::BigFloat for details on rounding modes, accuracy, precision, etc.)