You n me's got different dictionaries, Bean. I know in Spanish, e.g., carnicería, the i looks like it might be the penultimate syllable but an i followed by another vowel is normally just a glide and without the accent over the í it would be pronounced [car ni CER ya] (or [car ni ÞER ya], if you're speaking Old World Spanish); the accent indicates that the í gets full value of its own and thus *does become the penultimate syllable. I do not know if the same is true in Italian.
A quick look at the appropriate section of my dictionary and a check of an example indicates that, while the accents, both grave and acute, are used in normal writing of Italian, they are also used in the Italian to English section to indicate unexpected stress, even if they are not so used in the word itself. In the English to Italian section they seem to be used only as written in Italian. Unfortunately I cannot seem to find macelleria in the English to Italian section, neither under butcher anything nor meat anything.
