"Number of Digits Displayed SI declarations shall be shown in three digits except where the quantity is below 100 grams. If below 100 grams, the SI declaration may be shown in two digits. In either case, any final zero appearing to the right of the decimal point need not be shown."
21 CFR 101.7 says: "(d) The declaration may contain common or decimal fractions. A common fraction shall be in terms of halves, quarters, eighths, sixteenths, or thirty-seconds; except that if there exists a firmly established general consumer usage and trade custom of employing different common fractions in the net quantity declaration of a particular commodity, they may be employed. A common fraction shall be reduced to its lowest terms; a decimal fraction shall not be carried out to more than two places. A statement that includes small fractions of an ounce shall be deemed to permit smaller variations than one which does not include such fractions."
It seems to me that the CFR says you cannot go larger than 2 decimal points but that you do not need 2 decimal points, particularly if less than 100g. That being said, I would make sure to check with your state weights and measures. Michigan, for example, requires that 0 packages be under declared weighty by any amount. This is much more strict than the national standard. As such, we all, as manufactures tend to 'under promise, over deliver' to make sure we're meeting that requirement after accounting for natural variances in our industry. Also, if it's a regulatory auditor or government industry asking you to be more specific and list 2 decimal places you should consider the difficulty of granting their request. Sometimes we go along to get along, and all that, and arguing over 1 decimal point is not a hill that I, personally, am willing to die on.
There's my $0.03 cents