Assign cssClass after data.Rows.Add(row)

How do you assign the property of a column of a row when you add the row?
Here is the code that works but displays this row a different size and font:

DataTable data = dbAccess.getDataTable(con, table, sqlSv);
DataRow rowx;
rowx = data.NewRow();
dContent = Convert.ToDecimal(PriceTot);
sContent = dContent.ToString("###,###,###,###.#0");
rowx["Sub Total"]=sContent.ToString();
data.Rows.Add(rowx);
dg.DataSource = data;

However, cssClass is not a property of data, data.Rows, data.Columns, etc.
Then I assign the other rows the cssClass:

protected void OnItemDataBoundEventHandler(Object sender, DataGridItemEventArgs e)
{
     int iCtr = e.Item.Controls.Count;
     for (int i=0; i<iCtr; i++)
     {
      TableCell tcn = (TableCell) e.Item.Controls[i];
                tcn.CssClass = "clsListRecordHeader";
     }
}

BUT THIS DOESN'T PICK UP THE ADDED ROW -

Please HELP!