sub tounit($$) {
    # pick parameters
    my($num, $unit) = @_;

    # check parameters
    return undef unless looks_like_number($num);
    return undef unless looks_like_number($unit);
    return $unit unless $unit; # edit

    # round number
    my $res = $unit * sprintf( '%.0f', $num / $unit );

    # return rounded number
    return $res;
} # tounit