Can you perhaps show what you are trying to do because when I input say 9.5 for data, it will go there even if the x axis goes to 10. In general I have found that the axis will round up, but that has nothing to do with your data point, unless I am misunderstanding what you are trying to do (or asking).
Unless I am totally misunderstanding (which is completely possible) I would think that you could see that the data point appears midway between 15 and 16. Am I missing something. Can you upload an image of what you are talking about?