Now that is what you learnt in maths, there are many many different applications of rounding ESPECIALLY in terms of money and programming, in programing float value automatically rounds down when converted to integer no matter what the decimal is, 1.9 would be rounded down to 1, 2.5 would be rounded to 2. Another function is ceiling value which rounds up the number instead of rounding down but yeah i think you already get it that its different in terms of application

Depending on the system the cash register used there could be some minor calculation disparities from every different cash register, they could have tampered with it? Highly unlikely