Take the top coefficients from the website I linked to:
var h = 35.0;
var coeff = new float[] { 17, 12, -3 };
var easyCoeff = new float[] {-3, 12, 17, 12, -3};
var center = 2;
smoothed[x] =
((data[x - 2] * easyCoeff[center - 2]) +
(data[x - 1] * easyCoeff[center - 1]) +
(data[x - 0] * easyCoeff[center - 0]) +
(data[x + 1] * easyCoeff[center + 1]) +
(data[x + 2] * easyCoeff[center + 2])) / h;
The first 2 and last 2 points you cannoth smooth when using 5 points.