I said that I use USPS not UPS. As long as it is light enough to pass as a book, cd, software; use Media Mail. As a matter of fact you can use Media Mail for up to 10lbs and the price remains the same. Also, it is not like they are going to open your package and scrutinize it.
The only issue with media mail is it is a 10 cent difference from sending the item first class. I used media mail back in the day when I sold dvd movies. I had shipments that would take 14-27 days to deliver. Media mail is treated like usless products. And the delivery time is just as harsh. Feedbacks were poor on those items as well.
For 10 cents more I used First class mail and my shipment averaged 1-4 days in the USA and 6-9 Days air post for canada.
I would recommend you balance what means more to you. Delivery time or saving a few pennys.
Right now I sell in pretty high volume and alot of heavier items 10 pounds and up so I ship by FedEx . They have offered my company some bi discounts and give me alot of free services and equipment. Plus everything is tracked and insured.