Why do you need to have ó and not "o" in the word "dólar"? Per my understanding, in Spanish you accent a vowel only if the stress is not expected there according to the rule that the stress is the second-last vowel.
But here the "o" is the second last vowel anyway and the stress is expected on the "o", so why the "ó" with the accent?
In Spanish, the word "CLASE" and the word "TIPO", depending on the context, are synonyms, like in this case. "CLASE" means, besides "Lesson taught by a techer" (among many others) "ESPECIE" "CATEGORY", etc. It is normal to say that "el dólar es una clase, un tipo o una especie de moneda"