Use Math.Round

   
  

using System;

public class MainClass {
    public static void Main() {

        Console.WriteLine(Math.Round(4.4));
        Console.WriteLine(Math.Round(4.5));
        Console.WriteLine(Math.Round(4.6));
        Console.WriteLine(Math.Round(5.5));
        Console.WriteLine(Math.Round(4.54, 1));
        Console.WriteLine(Math.Round(4.55, 1));
        Console.WriteLine(Math.Round(4.65, 1));
        Console.WriteLine(Math.Round(4.56, 1));
    }
}