I can't give exact installation instructions for everyone because it somewhat depends on what you already have installed. You will need to add all the packages you need at the same time to avoid conflict messages as the packages are interdependent. Because this version of the package separated openssl-libs from the main package you will definitely need at least this one. You can see what's already installed by running rpm -qa openssl\*. If you have i686 packages installed as well, you will need to remove them or cross compile openssl for i686 as well, but we are getting deeper and deeper into the weeds and it's impossible to elucidate every corner case in this thread.
For me I had to do: cd ~/rpmbuild/RPMS/x86_64/; rpm -Uhv openssl-1.0.2k-21.el6.x86_64.rpm openssl-libs-1.0.2k-21.el6.x86_64.rpm openssl-devel-1.0.2k-21.el6.x86_64.rpm but this may not be the same for everyone.