private void dgv_CellValueChanged(object sender, DataGridViewCellEventArgs e)
        {            
            decimal nds = Convert.ToDecimal(1.18);

           if (e.RowIndex > -1 && e.ColumnIndex < ((DataGridView)sender).ColumnCount               
                && ((DataGridView)sender).Rows[e.RowIndex].Cells[e.ColumnIndex].Value != DBNull.Value)
            {
                if (String.Equals(((DataGridView)sender).Columns[e.ColumnIndex].DataPropertyName, "PRICE"))
                {
                    ((DataGridView)sender).Rows[e.RowIndex].Cells["PRICE_NDS"].Value
                       = nds * Decimal.Parse(((DataGridView)sender).Rows[e.RowIndex].Cells["PRICE"].Value.ToString());
                    
                  }
            }
        }