Building vertical scrolling portfolio

[kalam1ty]

I am trying to build an image portfolio that scrolls vertically, with 5 images in each row. As of now, each image has a width of 188px, with a 15px gap between each image. Totals to 1000px, the width of the container. So far this is working, but I have to make it so that each image will align itself to the image above it. It is very hard to explain, so here is a picture: http://i45.tinypic.com/1eq6o2.png

Here's the code as of now:

<div class="photos">
	<img src="pics/pic1.jpg" />
	<img src="pics/pic4.jpg" />
	<img src="pics/pic2.jpg" />
	<img src="pics/pic4.jpg" />
	<img src="pics/pic3.jpg" />
	<img src="pics/pic2.jpg" />
	<img src="pics/pic3.jpg" />
	<img src="pics/pic4.jpg" />
	<img src="pics/pic1.jpg" />
	<img src="pics/pic2.jpg" />
</div>

CSS:

.photos img:nth-child(5n) {  
	margin:0 0px 15px 0;
	padding:0;
}

.photos img {
	margin:0 15px 15px 0;
	padding:0;
	width:188px;
	float:left;
}

If you could help me out, I would really appreciate it. Thanks!