When multiplying and dividing, the final result can have no more significant figures than the least number of significant figures, in the numbers being multiplied, or divided.
Using your example, 3.079 * 102 * 0.068x10-1 = 2.1355944. 3.079 has four significant figures, 102 has three significant figures, and 0.068x10-1 has two significant figures. Leading zeros are not significant. You can see this by writing the number in correct scientific notation 6.8x10-3. Therefore, the answer can not be known beyond two significant figures, and must be rounded to two significant figures. Assuming that the units on 3.079 are also m, the result is 2.1 m3.
