Tender cuts that can be roasted in the oven without water come from parts of the animal that they don't use as much. Tender cuts come from the ribs for example. Anything labeled chuck is the most tough. Rump roast is tough. Roasts that are made from the round is in the middle but still needs moist heat. You can always ask the butcher.
And most basic cook books have diagrams.
Your roasts are probably hard and difficult to slice because you've cooked them for too long and with a more tough cut, not used moisture.
It's the acid in marinades that can somewhat tenderize cuts of meat. The cut does have to be in the marinade for an extended period of time. The amount of time depends on how thick the cut is. I doubt that a whole roast would benefit from marinade as a tenderizer but the marinade would add flavor.
The temperature varies. I rely on a cookbook for temperature because I rarely cook a roast. Some say a low temperature such as 275 for a longer period of time helps with tenderness. I don't know. You need a meat thermometer no matter what temperature you use.
Luvmywonderfullife gave you a couple of great recipes.
Later: I think J.L. is talking about roasting a tender cut of meat in dry heat in the oven without moisture on the meat its self. A wet roast would be one that is meant for a pot roast; a less tender cut that needs the moisture to help tenderize it. The two ways of roasting result in different tastes. However, one cannot dry roast a cut such as chuck and have a tender piece of meat.