I was going to write a post about the rpm’s and steps needed to install VirtualBox 5.0.x Guest Additions in a CentOS 7 virtual machine, but I found this article by LifeofaGeek. Check it out.  He is using the DKMS method which should keep things working even if you upgrade the kernel.  I may write another post with steps without DKMS for those who just want a streamlined process.