I'm a native speaker. I'm pretty sure that the plural of tabú is tabúes, I've seen it used in writing, in the press. For similar reasons that the plural of marroquí is marroquíes.
I argued with someone recently about the pluralization of menú. Observe that champú, tabú and menú are are all words of foreign origin that end in a tonic (accented u). Identical rules should apply to them. I now know that menús is correct (and so is Microsoft's documentation for Office in spanish). The question is: is menúes acceptable? incorrect? How do you pluralize: champú, tabú and menú? Can someone explain to me the definitive rule? Is it plagued with exceptions?