DataSet ds = new DataSet();
ds.ReadXml(@"D:xmlfile.xml");
dataGridView1.DataSource = ds.Tables[0].DefaultView;
dataGridView1.Tag = ds;   /* TAG */

string strTitle;
            string[] row = new string[] { strTitle, DateTime.Now.ToString("M/d/y"), "checked" };
            _parent.dataGridView1.Tag.Tables[0].Rows.Add(row);
            _parent.dataGridView1.Rows.Add();
            _parent.dataGridView1.DataSource = _parent.dataGridView1.Tag.Tables[0].DefaultView;

ds.Tables[0].Rows.Add(row)

string strTitle;
string[] row = new string[] { strTitle, DateTime.Now.ToString("M/d/y"), "checked" };
DataSet ds = (DataSet)_parent.dataGridView1.Tag;
ds.Tables[0].Rows.Add(row);

dataGridView1.DataSource = ds.Tables[0];

var dataTable = dataGridView1.DataSource as DataTable;
dataTable.Rows.Add(strTitle, DateTime.Now.ToString("M/d/y"), "checked");