using C5 for multiple domains on same server
Each domain will also need it's own MySQL database.
My suggestion would be to copy the concrete5 zip file and install on each domain yourself without doing the one click install - just in case (I never really trust those).
If of course you want five completely independent sites with different pages etc, then you need five separate installs, one click or otherwise.
Otherwise redirecting like someone mentioned here would be your best option.
Here is a guide from Dreamhost on how to setup domain redirection.