with a small tank you wil be looking at mbuna as a lot of haps etc will grow way too large, there are some dwarf mbuna species which grow no more than 4". Thing is, some of them are very aggressive and you will have to keep them in small numbers due to tank size, however they will be more aggressive in small numbers and aggression will be targeted at 1 or 2 fish.
As said, the dimensions of your tank are vital, a 90l hexagon tank would be useless, where a 90l tank 3ft (Ok, unlikely)long would be a lot better.
You may be Ok if you carefully select your species and keep one species, absolutley only 1 male in your tank or you may find bodies floating around your tank. A possible species may be yellow labs as they are one of the more peaceful mbuna.
Your question was 'Could I?' answer to that is probably! A better question may be 'Should I?'