Even if your game is free, it's not good to use copyrighted music. There are plenty of websites that offer free to use tracks.
I recommend these;
https://soundcloud.com/alcaknight most music here is available to freely use in VNs with credit
http://slos.biz/ for rules on usage, just click the top right corner "for English simply put", you are free to use so long as linked to http://sentive.net/ and they have a report form to fill in (they like to know what projects their music is in, that is all)
http://www.hmix.net/ of course credit