[rogue]

That's almost it. Try this:

{if $sales and $sales[sale].name|truncate:5 eq "Buy 3"}
   {include file="buttons/add_to_cart.tpl" style="button" href="javascript: if(FormValidation()) document.orderform.submit();"}
{elseif $sales}

{else}
   {include file="buttons/add_to_cart.tpl" style="button" href="javascript: if(FormValidation()) document.orderform.submit();"}
{/if}