Shake some salt onto a small plate or shallow bowl. Rub the rim of a rocks glass or margarita glass with a lime wedge. Dip the rim of the glass in the salt, and fill the glass with ice. Dip half of a lime wheel into a bit of Tajin and set aside (optional).

In a cocktail shaker, combine the reposado tequila, simple syrup, lime juice, the leftover wedge of lime, Triple Sec, cranberry juice, and a pinch of salt. Fill the cocktail shaker with a handful or two of ice. Cover, and shake vigorously until the outside of the shaker is very cold and frosty, about 20-30 seconds.

Strain the margarita into the prepared glass. Finish with a float of Grand Marnier (about 1 ounce). Garnish with a few cranberries and the Tajin-coated lime (or a regular lime wheel). Enjoy!