Yes, you absolutely can.
When you purchase a monthly subscription, a Dedicated IP option is available for purchase. Currently the additional cost of a private IP is $9.95 / month + a 5% volume charge based on the value of your subscription.
A dedicated IP gives you an address to send from that is only affected by what you send from it, as opposed to sharing a sender IP with many others in an ordinary situation. This is useful if you want to avoid the risks of your IP being brought down in reliability or rating because of someone else's spam.
As noted above, it is not explicitly included, but when you purchase any monthly subscription you are given the option to purchase a dedicated IP address along with it.