The answer to your question is, "it depends."

If you know what form the function should be (polynomial, logarithmic, sinusoidal, etc.) then the answer is probably yes. You can usually do some kind of linear regression, or log-log plot, or something to determine the parameters. However if you don't know the form of the function ahead of time, all you can do is guess at the form and hope for the best.

The nice thing is that if you don't care about anything except for modeling the points you have, then you can always fit your data to a sufficiently high polynomial function.

Now whether your calculator can best fit your data to, say, a sinusoidal curve is going to depend on the kind of calculator and the software you can get for it.

-Dan