Keep in mind that many of those "odd figures" are due to the fact that euro collector coins can, by law, not have the same denominations as circulation and commemorative coins. Ah well, since the collector pieces are not supposed to be used for everyday payments anyway (and most of them are surcharged pieces), that does not really matter.

I think that the idea, initially, was that the national mints would simply issue collector coins with high denominations. This way you would have had the 1 cent to 2 euro "range" for circulating pieces, and €5, €10, etc. could have been for collector coins. Well, some mints came up with lower face values very soon, issuing brass or Cu-Ni 1.50 or 2.50 pieces. And it went on from there. When Austria started issuing their glow-in-the-dark pieces, they picked €3 as the denomination for that series ...
Christian