Are you getting an error or is nothing happening? If there's no error, it may just be that the grid is not showing the insert. If you refresh the grid, if an insert was successful, it will show.
I'd also make sure you are setting the right value for SalesReceiptRecordID. You should be using "Value from Screen" and the field RecordID. If the value is wrong, it won't show in the grid. Since the grid is attached to the screen, it will only show records belonging to that sales receipt.
You could use the Import/Export Tool and export the SalesReceiptLine table to see if the inserts were actually done and if so, what values they have.
- Adam