<table width="100%">
  <tr>
    <?php
    $count = 1;
    foreach($arraymitbildas as $bild) { // oder while
      if($count <= 5) {
        $count++;
        echo '<td width="20%"></td>';
      } else {
        echo '</tr><tr>';
        echo '<td width="20%"></td>';
        $count = 1;
      }
    }
    ?>
  </tr>
</table>