Check the Nevada Taxi Cab Authority Web site (https://taxi.state.nv.us/FaresFees.htm). The Mirage is approximately 4 miles from the Golden Nugget. The most direct route (shortest mileage) would be Main Street to Las Vegas Blvd to the Mirage. Depending on time of day and traffic, I might take a slightly different route using Industrial Road as I try to avoid Las Vegas Blvd at all costs, but as far as most direct route, the way I outlined is it.
If you are the tour guide and they are interested in it, you may want the taxi to go up Carson from the Golden Nugget to Las Vegas Blvd. That way you will pass the Gold and Silver Pawn Shop (the store in "Pawn Stars") and the Little White Wedding Chapel (used the "The Hangover") on your way to the Mirage.
Larry (Limo Driver) from Las Vegas