"Тридцять шість гривень"
I think, there should be such a post. If you write one, I'll give you several lingots (that's all I can do for you now). I'm a native Ukrainian speaker, but I would be extremely disappointed if I were left with "it's far too complicated, don't bother yourself with it". We all are here to learn, and everyone's needs are different: there are businessmen or tourists who need a basic grasp, and there are linguists who want nitty-gritty details. Anyway, good luck with the post!
There are three endings a genitive plural can get: -ів, -ей, and no ending. Feminine nouns almost never get -ів, masculine never get zero ending, apart from that the rules get a bit murky.
In case of гривня, you have a zero ending, then you have to use a soft sign (ь) to preserve in writing the palatisation of н, and then you add an e as an extra vowel to make it pronounceable.
The extra vowels in Ukrainian are о and е. I suspect е is used near palatalised consotants and о otherwise, but I bet there are counterexamples to that.
Yeah, that's stupid that some answers get accepted even though they should not. On the other hand, it works for English and some other European languages where 3 is something like "tre"/"tri", same as in Ukranian and Russian. I mean, they are really hard to screw up unless it is a typo :)