Problem with Math.Tan Function

Question

[code]
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Testing_Binary
{
    class Program
    {
        static void Main(string[] args)
        {
            Double Radian = (Math.PI / 180);
            Double count = 0;
            int[] array = {1,0};
            for (int i = 0; i < 2; i++)
            {
                if (array[i] == 1) count += Math.Tan(Radian);//POSITIVE COUNT = 0.0174550649282176
                if (array[i] == 0) count += Math.Tan(-Radian);//NEGATIVE COUNT = -0.0174550649282176
            }
            //EXPECTING POSITVE AND NEGATIVE TO CANCELL EACH OTHER AND COUNT = 0, BUT GOT THE FOLLOWING:
            Console.WriteLine("count = {0}", count);//I DON'T UNDERSTAND WHY = -4.06575814682064E-20
            //I REALLY NEED TO UNDERSTAND WHAT HAPPEN. CAN SOMEONE PLEASE EXPLAIN?
        }
    }
}
[/code]