I assume that unescaping in Handlebars works the same as in vanilla Mustache.
In that case use triple mustaches to unescape html, i,e: {{{unescapedhtml}}}
, like:
<script id="quiz-result" type="text/x-handlebars-template">
{{#each rounds}}
{{{round_end_result}}}
{{/each}}
<div class="clear"></div>
for ref see:
http://mustache.github.com/mustache.5.html