Assuming your lines are in an array that you're echoing, something like this would work:
$count = 0;
$div = 1;
foreach($lines as $line){ //or a for loop, whatever you're using
if(0 == $count){
echo "";
}
$count++;
echo $line;
if(10 == $count){
echo "
";
$count = 0;
}
}