You can do exactly what are you asking in this way
$counter = 0;
$length = count($array);
foreach ($array as $value) {
$counter=$counter+1;
for ($stepvvx = 10; $stepvvx <= 100; $stepvvx=$stepvvx+10)
{
if ($counter==intval(($length*$stepvvx)/100)){
echo "
$stepvvx %";
}
# do your task here
}