Can one also say "ten euro" instead of "ten euros" ?
If I am correct one has to say "ten dollars" and not "ten dollar" ?
"10 euro" is also correct, at least according to my dictionary, but "10 euros" sounds better. And I don't think you have to capitalize "euro."
Not a teacher.
The ticket cost ten Euros.
It is a ten Euro ticket.
Note: the dictionary might not mention adjectives but just give an acceptable example (which happens to be an adjective).
(Note: in informal speech the S can be dropped in some cases: "Ten quid? It's not worth a fiver." But I've never heard 'Euro' used like this; maybe I would have - if we used it more in the UK.)