I would suggest another possibility for either the “rounding up” or the lousy math, take your pick. In the Torah and elsewhere, 70 is traditionally a number of completeness, of wholeness, being comprised of 7 (as in the days of creation) times 10 (Commandments, Minyan, etc.). Indeed, after all the divisiveness which has occupied this family up to now, the fact that the family is reunited, prosperous, and at relative peace is noteworthy. Consider this: this is the fifth time in the Torah that the phrase B’nai Yisrael, (the Children of Israel) is used in reference to the actual children of the original Israel, Jacob. The name will be used in this fashion only twice more; thereafter it will refer to the nation, not the family. That’s right. A total of 7.
Shabbat ShalomRabbi/Hazzan David B. Sislen