I am often amazed to see a strange pattern in a seemingly mundane day-to-day activity, a pattern whose logic I simply can't understand. I would appreciate if you could help me understand this.

While shopping, at the time of paying our bills in cash, the balance is returned by the cashier /counter-person in such a manner that all the cash notes are arranged in one sequence except the last note. For instance, if you shop for items worth Rs. 100/- and pay through a Rs. 1000/- note, the concerned person while returning 9 hundred rupee notes to you would arrange eight notes with Gandhiji's photo on one side and water-mark on the other, but would reverse the pattern for the last note. Is it done as a good-luck charm or is it as per some accountancy principle?
Even most ATMs dispense money in a manner that all notes have 'Gandhiji-watermark combo' in one pattern, but the pattern is reversed for the last 5 notes of Rs. 100/- denomination. Do you know why?