ASP.Net GridView Export to Excel: Round Decimal numbers to two decimal places

Please run this code

HTML

<form id="form1" runat="server">
<asp:GridView ID="GridView1" HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White"
    RowStyle-BackColor="#A1DCF2" AlternatingRowStyle-BackColor="White" AlternatingRowStyle-ForeColor="#000"
    runat="server" AutoGenerateColumns="false" AllowPaging="true" OnPageIndexChanging="OnPageIndexChanging">
    <Columns>
        <asp:BoundField DataField="ContactName" HeaderText="Contact Name" ItemStyle-Width="150px" />
        <asp:BoundField DataField="City" HeaderText="City" ItemStyle-Width="100px" />
        <asp:BoundField DataField="Salary" HeaderText="Salary" ItemStyle-Width="100px" />
    </Columns>
</asp:GridView>
<br />
<asp:Button ID="btnExport" runat="server" Text="Export To Excel" OnClick = "ExportToExcel" />
</form>

Namespace

using System.IO;
using System.Data;
using System.Drawing;
using System.Data.SqlClient;
using System.Configuration;

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        this.BindGrid();
    }
}

private void BindGrid()
{
    DataTable dt = new DataTable();
    dt.Columns.AddRange(new DataColumn[3] { new DataColumn("ContactName", typeof(string)),
                        new DataColumn("City", typeof(string)),
                        new DataColumn("Salary",typeof(string)) });
    dt.Rows.Add("Maria", "Boise", "2,874444");
    dt.Rows.Add("Ana Trujillo", "Warszawa", "3,500000");
    dt.Rows.Add("Antonio Moreno", "Mannheim", "3,600000");
    dt.Rows.Add("Thomas Hardy", "Madrid", "4,650000");
    GridView1.DataSource = dt;
    GridView1.DataBind();
    ViewState["Data"] = dt;
}

protected void OnPageIndexChanging(object sender, GridViewPageEventArgs e)
{
    GridView1.PageIndex = e.NewPageIndex;
    this.BindGrid();
}

protected void ExportToExcel(object sender, EventArgs e)
{
    Response.Clear();
    Response.Buffer = true;
    Response.AddHeader("content-disposition", "attachment;filename=GridViewExport.xls");
    Response.Charset = "";
    Response.ContentType = "application/vnd.ms-excel";
    using (StringWriter sw = new StringWriter())
    {
        HtmlTextWriter hw = new HtmlTextWriter(sw);

        //To Export all pages
        GridView1.AllowPaging = false;
        DataTable dt = (DataTable)ViewState["Data"];
        DataTable dt2 = new DataTable();
        for (int i = 0; i < dt.Columns.Count; i++)
        {
            dt2.Columns.Add(dt.Columns[i].ColumnName);
        }
        for (int i = 0; i < dt.Rows.Count; i++)
        {
            dt2.Rows.Add(dt.Rows[i]["ContactName"].ToString(), dt.Rows[i]["City"].ToString(), dt.Rows[i]["Salary"].ToString().Substring(0, 4));
        }

        this.GridView1.DataSource = dt2;
        this.GridView1.DataBind();

        GridView1.HeaderRow.BackColor = Color.White;
        foreach (TableCell cell in GridView1.HeaderRow.Cells)
        {
            cell.BackColor = GridView1.HeaderStyle.BackColor;
        }
        foreach (GridViewRow row in GridView1.Rows)
        {
            row.BackColor = Color.White;
            foreach (TableCell cell in row.Cells)
            {
                if (row.RowIndex % 2 == 0)
                {
                    cell.BackColor = GridView1.AlternatingRowStyle.BackColor;
                }
                else
                {
                    cell.BackColor = GridView1.RowStyle.BackColor;
                }
                cell.CssClass = "textmode";
            }
        }

        GridView1.RenderControl(hw);

        //style to format numbers to string
        string style = @"<style> .textmode { mso-number-format:\@; } </style>";
        Response.Write(style);
        Response.Output.Write(sw.ToString());
        Response.Flush();
        Response.End();
    }
}

public override void VerifyRenderingInServerForm(Control control)
{
    /* Verifies that the control is rendered */
}

Screenshot