rounding up something usually has a borderline around the middlevalue, quite often that includes the number 5 since it often lands in the middle.
if we take 654 and round it up to the nearest hundred, well, 654 is between 600 and 700, but is closer to which one? Well, the middlevalue of 600 and 700 is 650, and 654 is just 4 units above that, so it's really already on the 2nd half of 600 and 700, so it'll round up to 700.
if we try to round 654 to the nearest ten, then we have to look at the "54" part only, 54 is between the 50 and 60, but is closer to which one? Well, the middlevalue of 50 and 60 is 55, and 54 is below 55, so is closer to 50, thus its rounding up will be 650.
so Archie needs to pay a closer eye to that middlevalue.