That's 4%, that's not a significant amount for functional purposes and it's a whole number to whole number conversion. Most of the time, if I'm converting, it's from metric to imperial so 1 km is 0.62 miles. If you tell me the speed limit is 70 km/h it's way easier for me to calculate 70 ÷ 5 x 3 = 42 mph than to calculate either 0.62 x 70 or 70 ÷ 1.6 = 43.49.