Use a 6-quart slow cooker. Place the pork roast inside the slow cooker insert and rub all sides with cumin. Pour in the salsa and the juice from 3 of the limes.
Cover and cook on low for 8-10 hours, or on high for about 6 hours. Shred the meat completely using two large forks. If desired, stir in the fresh cilantro.
Serve in corn tortillas with a lime wedge and your favorite toppings.
Notes
Nutrition facts not calculated with tortillas or toppings, as this will vary based on individual serving preferences. Nutrition facts may vary based on the type of salsa used, as well.