Not some chemists, all chemists.
Some medications come in packets of 7 or 28 tablets that are difficult to split. I am on a medication that I only take once a week, so I can't get a 30 day prescription. Either way, it doesn't matter, it your medication cost more than €144 a month, they cannot charge you €144 13 times, even if they dispense it in 28 day packets.
In my case, the chemist gives me 5 weeks medication some times, but if I want a full months tablets on the 28th of the month, I get them but I pay for the next months fee.