I think this is a play on words. If I’m not mistaken, “dia sim, dia não” is a common expression that means “every other day”.
So here, they are saying “dia sim, dia SIM”, as a mildly unexpected twist, to mean that every single day, there are savings.
ps. if anyone from Pingo Doce wants to get in touch about compensating us for this free unsolicited promotion… cerveja and gelado are among our many forms of preferred payment 