This is the place. Now known as La Rosita. The grocery selection is fine, great hot sauce selection BUT go on a Saturday or Sunday when you can order freshly prepared taqueria food as good as any I've ever had, and I lived on Milwaukee's south side most of my life.
The carnitas are terrific, just had to say it. I bounce from the torta with your choice of meat (and bear in mind this is a butcher shop, so they make their own barbacoa and carnitas and marinated chicken, lengua, etc), to huaraches when you can get them, to just a simple soft taco. This is the real deal, no Taco Bell Doritos taco here. At $1.75 a taco, and they're huge, wow. Oh, and the salsas they make are great, the red has a mighty nice zip.
Oh, final word - house made chorizo. Holy crap. OK, that was five words, but it's unlike any I've had before. Complex, perfectly spiced, a slight hint of cinnamon, not greasy, simply great. You can order it on to-go food at the taqueria on weekends, or by the pound in their butcher shop (raw). I use half, freeze half.