"There's no need to settle for 30-second clips to decide if you want to buy a song," said Chris Gorog, CEO of Napster.
"For five bucks now you can have access to our entire music catalog and get five MP3s to add to your permanent collection," he added.
The Best Buy subsidiary previously charged $US13 per month for the streaming service.
The main shortcoming is that the new $US5 subscription only allows streaming to a computer. Anyone wanting to listen on a mobile device such as a smartphone must instead choose the $US15 Napster To Go service. Only a limited range of devices is supported, and Apple's still hugely popular iPod family isn't among them.
The MP3 downloads offered as part of the monthly fee will play on iPods, however.
It seems that part of the strategy is to sell Napster subscriptions at Best Buy stores, perhaps as a "would you like fries with that" upsell to buyers of personal computers and media players.
Napster sparked the file-sharing revolution in 1999, but legal action from music companies saw its demise two years later. Acquired by Roxio, the company reappeared in 2003 as a music subscription service with the blessing of the recording industry. It was acquired by Best Buy in September 2008.
Subscription services have met with a mixed response from their target customers. Some people are happy to pay a modest monthly fee for legal access to a wide range of music including new releases.
Others - perhaps an older demographic? - prefer to pay for just those songs and albums that they actually want to keep, and expect unrestricted access to them.
The trend for ISPs to impose monthly caps or charge in proportion to the amount of data downloaded could work against streaming services.