Does every Japanese word, when in romaji, always end with an "n" or a vowel, it seems that way?

Yes. There are 46 characters in hiragana/katakana, and can be combined to made an additional handful of sounds. All, however, end in an a, e, i, o, or u. Possible consonants include k, s, t, n, h, m, y, r, and w, but every consonant must be followed by a vowel with the exception of "n", which can stand alone.