I would think you need them for the time you have the car. This way you can show how well you’ve kept up with maintenance. This says a lot to someone if you ever sold it.

You keep them until you sell or trade in your car , You can actually sell it for more when you have all the maintenance records for the car… and it means alot to who ever gets the car from you to see what all you have had done to it and when

Put it all into a folder with the date and mileage on it. You don’t need the exact receipts. But the records are invaluable when selling.