If all you want is the Regno, ST_Name, and FeeAmount columns, and you want the FeeAmount columns totalled, then use this query:
Dim strSQL6 As String = "SELECT FeesTransaction.Regno, FeesTransaction.ST_Name, sum(FeesMaster.FeeAmount) as FeeAmount FROM FeesTransaction INNER JOIN FeesMaster ON FeesTransaction.Regno = FeesMaster.Regno WHERE FeesTransaction.class='" & cboClass.Text & "' and FeesTransaction.section='" & cboSection.Text & "' and FeesTransaction.FeeType='" & cboFeeType.Text & "' GROUP BY FeesTransaction.Regno, FeesTransaction.ST_Name"
This assumes that all 3 columns are already on your datagridview, as per your last statement.
Thanks,
-Bert