No one maintains perfect nutrition. In fact, to set such a goal would be to set yourself up for failure. Instead, think of nutrition as a balancing act between what you want to eat and what you should eat. Focusing too heavily on the "should" side will set you up for failure and guilt, while focusing only on what you want will pile on the pounds and make you less healthy.
Remember that vitamins are nothing more then supplements. You want to make sure you are eating healthy throughout the day rather than just taking vitamins all day. You should only take one dose of multivitamins in a given day. The rest of your nutrients should come from the food you eat throughout the day.