Magento: first last class or ul tag after 5 products

<ul class="products">
<?php
$i=0;
foreach ($collection as $_product) { $i++; ?>

<li class="item <?php if($i==1) { echo "first";} if($i%5==0) { echo "last";}?>  ">
<a class="product-images" href="<?php echo $_product->getProductUrl() ?>"><img src="<?php echo $this->helper('catalog/image')->init($_product, 'small_image'); ?>" width="200" height="200" alt="" /></a>
<a href="<?php echo $_product->getProductUrl(); ?>">
<span class="custom-name"><?php echo $_product->getName(); ?></span>
</a>
<span class="custom-price"><?php echo  Mage::helper('core')->currency(number_format($_product->getPrice(),2)); ?></span>

</li>
<?php if($i%5==0)
{ ?>
</ul><ul class="products <?php if($i%5==0) { echo "last";} ?>">
<?php
}?>

<?php  } ?>
</ul>