Picking up pennies

If you drop a penny on say the sidewalk do you pick it up? If you see one someone else dropped do you pick it up? Is the urgency the same? At what point will we no longer feel " a penny saved is a penny earned" as part of the question?
My own experience is a penny is just on the dividing line and can be used to pay sales tax. I don't feel as obligated to pick up one someone else dropped.