If i understand you correctly you want to increase
ReciptNumber
for each selected row in DataFridView. So, you need only one loop:
Dim ReciptNumber As Integer = 0
Dim mixReciptNumber As Integer = ReceiptEntryTableAdapter1.ScalarQuery1("BILL")
ReciptNumber = mixReciptNumber
For Each Row As DataGridViewRow In DataGridView1.SelectedRows
ReciptNumber = mixReciptNumber + 1
Next