Made some changes to static files (css for example), but Apache/nginx on your Vagrant VM still delivering the old version or even corrupted files? Then you should turn off sendfile() in your Apache/nginx configuration!
Simply spoken, sendfile() uses kernel calls to copy files directly from disc to tcp. If you are using remote filesystems (like nfs or the VirtualBox Guest Additions stuff), this method isn't reliable.
You can find more info about sendfile() in this techrepublic article.
To turn off sendfile() in Apache, you can use the
EnableSendfile off directive, for nginx use