Some journals have a policy to make all reviews available to all parties involved (Referees and Authors), so the practice is not uncommon.
Some journals have a policy to not make the reviews available to all Referees. In this case I think to request it of a curiosity is quite unorthodox. The decision to accept / reject the paper is made by the Editor, who consults the Referees for their expertise in a particular area. As a Referee, I would expect my opinion to be heard by the Editor, but other than that, I do not assume the Editor to be obliged to make a decision I recommend and/or to explain the decision to me.
Some (smaller) journals do not have a policy re this question. In this case you could try to very politely ask about it. Politeness is a key.