SqlBulkCopy Excel Import: Decimal Precision lost and its rounded in C# .Net

You will need to define data types for columns in your DataTable. I create a small sample to help you out

SQL

CREATE TABLE [dbo].[tblPersons](
	[PersonId] [int] IDENTITY(1,1) NOT NULL,
	[Name] [varchar](100) NOT NULL,
	[Salary] [numeric](10, 3) NOT NULL
) ON [PRIMARY]

GO

Namespaces

using System.Configuration;
using System.Data.OleDb;
using System.Data.SqlClient;
using System.Data;

Code

protected void Page_Load(object sender, EventArgs e)
{
    string excelPath = Server.MapPath("~/Files/Persons.xls");
    string connString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + excelPath + ";Extended Properties=;Excel 8.0;HDR=YES;IMEX=1";
    using (OleDbConnection excel_con = new OleDbConnection(connString))
    {
        excel_con.Open();
        string sheet1 = excel_con.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, null).Rows[0]["TABLE_NAME"].ToString();
        DataTable dtExcelData = new DataTable();
        dtExcelData.Columns.AddRange(new DataColumn[3] { new DataColumn("Id", typeof(int)),
                    new DataColumn("Name", typeof(string)),
                    new DataColumn("Salary",typeof(decimal)) });
        using (OleDbDataAdapter oda = new OleDbDataAdapter("SELECT * FROM [" + sheet1 + "]", excel_con))
        {
            oda.Fill(dtExcelData);
        }
        excel_con.Close();

        string consString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
        using (SqlConnection con = new SqlConnection(consString))
        {
            using (SqlBulkCopy bulkCopy = new SqlBulkCopy(con))
            {
                bulkCopy.DestinationTableName = "dbo.tblPersons"; // Table Name
                bulkCopy.ColumnMappings.Add("ID", "PersonId");
                bulkCopy.ColumnMappings.Add("Name", "Name");
                bulkCopy.ColumnMappings.Add("Salary", "Salary");
                con.Open();
                bulkCopy.WriteToServer(dtExcelData);
                con.Close();
            }
        }
    }
}

Screenshots