Custom Field value sorting

Hello and thanks for looking into my post!

I have a bunch of values for the same custom field name.
I would like to display the custom fields in ascending alphabetical order.
Right now they are showing in the order I entered them. Any ideas?

Custom fields
name – purchase, value – purchase-itunes
name – purchase, value – purchase-amazon
name – purchase, value – purchase-emusic

here is the code I am using:

<?php $value = get_post_meta($post->ID, 'purchase', false); ?>

	<ul class="purchaseLinks">
		<?php foreach($value as $value) {
			if($value == 'purchase-itunes') {
		echo '<li><a href="#">itunes (Mp3)</a></li>';
	}
	elseif($value == 'purchase-amazon') {
		echo '<li><a href="#">Amazon (Mp3)</a></li>';
	} 

	elseif($value == 'purchase-emusic') {
		echo '<li><a href="#">emusic (Mp3)</a></li>';
	}

else {
		echo '';
	}

			} ?>
	</ul>