I thought I may have misremembered as it’s a few years since I’ve been to Luz so I asked my other half and he remembers the shop to. Whether it’s there now I’ve no idea but it certainly would have been in 2007.
The only commercial business near the Millennium is the Mirage, located just south. The Mirage is mentioned several times in the PJ-Files. It is a restaurant/pub, hardly the place Totman would carry a child to.
Baptista was shut, due to the lateness of the hour. That leaves two Ali Super mini markets, and O Celeiro mini market, none in the direction that Tannerman was heading.
My info comes from someone who has documented facilities in Luz (shops, bars, cafes, restaurants) from before the time Madeleine disappeared.
If you still believe there was a shop near the Millennium, you will be able to find it on Google StreetView.
By the way. It's a fair old trek from block 4 to the Millennium. So why was Totman toting his child? Much easier just to leave the child at 'home', surely?