I agree that it says Grocer &c, and as he was getting older, I wouldn't want to rule out a change from being a groom. On the other hand, it could be that he wrote Groom on the form, and the enumerator misread it when copying it into the book.
If you look at the summary pages for that district you should find the enumerator's signature. Can you work out if he is likely to have known William Raynes personally, and thus the likelihood of a mistake?
Also, if William's death, burial or probate records show that he was a groom when he died, that seems to increase the chances of this 1841 entry being a copying error.