No, don't rely on that. The number of digits determines resolution - how fine a difference can you detect and measure? That is not the same as accuracy, which is how close to "true" is the reading? You could have a digital multimeter with a 5-digit display but a 10% low bias on all readings.
Number of digits is a guide in the sense that most makers of cheap meters with questionable accuracy would not spend the money top put in more display digits, but some do to fool you.
Actually, your question is hard to answer. You can just take the word of the makers as written in specifications, and that's probably OK. But if you want to test it and be sure, you need to find some very accurately know voltages, currents, resistances, etc., and they are not easy to come by. For that your best source MIGHT be the engineering school you go to. Although they won't put the really good stuff out for first-year students, the lab staff may be willing to let you use their good meters under supervision just to compare against yours.