Without seeing what you’ve got so far, it’s hard to be sure, but it sounds like you need to reduce padding and/or margins on the list item and/or the list itself.
If you want a cross-browser solution, the easiest one is to just put an ID on the last item and then put :after {content:none;} on that ID.
the previous problem:
making a block element an inline-block element was causing a right whitespace to appear. that was from the whitespace in the actual markup. so, no whitespace between the end tag and the start tag of between elements fixed it (…</div><div>…, no new line or spaces there).