Meals per diem deduction

While out of town on business, does it matter rather you spend more or less per day than the standard per diem rate if all you want to do is take the simple approach and use the daily per diem rate?  In other words, if the per diem rate was $65 per day and one day you spent more and another day you spent less, can you still claim $65 for the day that you spent less?  I realize you might want to keep track of actual expenses for the trip and use whichever method resulted in the larger deduction.  Basically the question is can you spend less than the per diem rate, but still claim the per diem rate?