In a stainless steel or enameled skillet cook the onion and the garlic in the oil over moderate heat stirring for 5 minutes, or until they are soft. Stir in the ground round, salt, and chili powder, and saute the mixture over moderately high heat, stirring until the beef is brown. Stir in the chili sauce and the cumin and drain the mixture in a fine sieve. (The beef mixture may be made up to 1 day ahead, cooled, and chilled, covered. Reheat the mixture in a saucepan over low heat, stirring.)
Halve the tortillas and steam them in batches in a steamer set over boiling water for 1 minute, or until they are pliable. Bend the tortilla halves into cone shapes and secure them with a toothpick.
Fill a deep fryer with 4 inches of oil and heat to 375 degrees F.
Using tongs, hold cone at the tip and gently place into the oil with the opening of the cone facing down. Fry the cones in small batches for 1 minute or until crisp and golden. Transfer to paper towels to drain. Let the cones cool slightly then remove the toothpick carefully. The tortilla cones may be made up to 3 days ahead and stored in an airtight container. Reheat the cones, if desired.
Put some of the shredded romaine in each cone, top it with some of the beef mixture, and garnish the tacos with the cheddar and tomato. Arrange the remaining romaine in a serving dish and nestle the taco cones in it carefully so that they stand upright.