sub round2($$)
{
my $var=$_[0];
my $decimal=($var-int(var));
if ($decimal && ((length($decimal)-2)>$_[1]) && ($var=~/5$/))
 {                                           
 $var=~s/5$/6/;
 }
sprintf "%.$_[1]f",$var;
}

# some output:
for (my $i = 1; $i < \xFFFF; $i <<= 1)
 { print round($i+0.555,2), "  ", round2($i+0.555,2), "\n"; }