*headdesk* Don't listen to me when I've been doing code all day, seriously.

I meant:

.module-tags_multilevel ul li

and

.module-tags_multilevel ul li li

The .tags would be for the tags page, not the module. The non-link-tag will work too, though, if none of your top-tier items have anything in them. So, if foo only ever exists to be a header, and nothing is ever tagged foo, yeah, that'll do it.