Finished programming an assignment, what could I do better?

I am posting this because I always feel like I Could do something better with my code. I feel like I'm too elementary, do you have any suggestions about what I can do better? (This is my first time posting, so I hope this is a suitable question and wont get flagged.)

Main Method Side

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace InternetMerchandise
{
    class Program
    {
        static void Main(string[] args)
        {
        // Declaring Variables and Methods
            double totalPurchases;
            totalPurchases = GetTotalPurchases();
            ShippingCost MyCost = new ShippingCost(totalPurchases);

        // Results for showing shipping charges

            MyCost.SetCharges(totalPurchases);
            Console.ReadLine();
            Console.WriteLine("The Shipping Charges is: {0:C}", MyCost.ShippingCharges);
            Console.ReadLine();   
        }

     // method to obtain Total Purchases
        public static double GetTotalPurchases()
        {
            double totalPurchases;
            Console.WriteLine(" Enter the Price of goods purchased\n ");
            totalPurchases = double.Parse(Console.ReadLine());
            return totalPurchases;
        }
   }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace InternetMerchandise
{
    class ShippingCost
   
        {
            private double shippingCharges;
            private double totalPurchases;

        // Default Constructor
            public ShippingCost()
            {
            }

        // Constructor with One argument
            public ShippingCost(double price)
            {
                totalPurchases = price;
            }

        // Getters and Setters
            public double TotalPurchases
            {
                set { totalPurchases = value; }
                get { return totalPurchases; }
            }

            public double ShippingCharges
            {
                set { shippingCharges = value; }
                get { return shippingCharges; }
            }

        // Determine how much customer is to be charged per purchase price
            public void SetCharges(double totalPurchases)
            {

                if ((totalPurchases > 0) && (totalPurchases <= 250))
                    shippingCharges = 5;
                else if
                    ((totalPurchases > 250) && (totalPurchases <= 500))
                    shippingCharges = 8;

                else if ((totalPurchases > 500) && (totalPurchases <= 1000))
                    shippingCharges = 10;
                else if
                    ((totalPurchases>1000) && (totalPurchases <= 5000))
                    shippingCharges = 15;

                else if ((totalPurchases > 5000))
                    shippingCharges = 20;

            }
        }
    }