The key to consider is the fact that you are dealing with "round primals." Just because the name of a cut of meat is followed by the word "steak" it does not necessarily mean that it is suitable for all cooking methods. Just as most beef round cut  steaks should be braised, so should most venison round steaks.
    If you are experiencing "tough" cuts off the round my guess is that you fried, grilled, or broiled them. Next time try dipping them in a mix of flour and seasoned salt, brown in hot oil on both sides, reduce the heat to simmer, add a sauce of your choice, cover and simmer until tender. Serve over/with pasta or rice.
    The best round cuts for grilling would be the Top Round and Sirloin Tip.
I would recommend marinating overnight in the refrigerator or use a commercial meat tenderizer on them.
    I only come up with five round primals: Top, Bottom, Eye, Heel, and Sirloin Tip. If you're counting Top Sirloin that's actually part of the loin.
    By the way, the heel is only suitable for grinding.

Thanks for visiting,

    Dave & Ruth
    D & R Processing

PS. Ruth and I have gotten spoiled because of our "vacuum tumblers". We can vacuum marinade the round cuts and grill all of them because of the tenderizing effect of the combination of marinades and tumbling.