Yes, this feature is called a Domain Alias. By setting up Domain Aliases users can reach your website through more than one domain name. Before creating additional Domain Aliases there are a few things that you should be aware of:
Domain Aliases will not hide your website's "real" domain name. When users come to your website through an aliased domain name their browser's address bar will often change to show the "real" domain name.
Domain Aliases share the same email setup as the "real" domain that they point to. For example, if you had a website named "example.com" and you added "example.NET" as a Domain Alias then all email sent to johndoe@example.NET would deliver to the same place as if the user had sent to johndoe@example.COM.
In order to setup a new Domain Alias you must ensure that the new domain name is using our Name Servers (ns.dnsbox.net and ns2.dnsbox.net). If your domain name was registered through http://domainrocket.com/DomainRocket.com then it should already be using the right Name Server.
You can setup Domain Aliases directly through the ServerTools Control Panel. Just login to ServerTools and click on the "Utilities" menu option and there you will find the "Domain Alias Manager".
If this is your first Domain Alias then you will be prompted for a domain name. Enter the domain name that you would like to setup as an alias. As long as the domain name is using the correct name servers, it should be active within about an hour. One exception to that would be if the domain name was just recently registered (It takes 24 hours for a domain name to become active after it is registered).