You need to comment out the white space between the elements, like so:
<div class="tile-container">
<div class="tile-large">1</div><!--
--><div class="tile-wide">2</div><!--
--><div class="tile-small">3</div><!--
--><div class="tile-small">4</div><!--
--><div class="tile-small">5</div><!--
--><div class="tile-small">6</div><!--
--><div class="tile-wide">7</div><!--
--><div class="tile-large">8</div>
</div>
DEMO: http://jsfiddle.net/P7cbA/11/
Another way is to put the elements in the HTML in one line without any spaces between them, but this reduces the code readability:
<div class="tile-container">
<div class="tile-large">1</div><div class="tile-wide">2</div><div class="tile-small">3</div><div class="tile-small">4</div><div class="tile-small">5</div><div class="tile-small">6</div><div class="tile-wide">7</div><div class="tile-large">8</div>
</div>