You can calculate 3444 times 670 without rounding or you can estimate it WITH rounding. But you cannot estimate it without rounding.
670 is ten times bigger than 67.
In decimal form, 8.93 times, with the 3 repeating. In fraction form, 8 and 14/15 times, or 134/15 times.
8 times with a remainder of 70
670
230 + 670 = 900