19 CFR § 159.3 - Rounding of fractions.
(a) Value. In the computation of duty on entries, ad valorem rates shall be applied to the values in even dollars, fractional parts of a dollar less than 50 cents being disregarded and 50 cents or more being considered as $1, with all merchandise in the same invoice subject to the same rate of duty to be treated as a unit. However, the total dutiable value of the invoice shall not be increased or decreased by more than the rounding of the total dutiable value to an even dollar. When necessary, fractional parts of a dollar, whether more or less than 50 cents, shall be dropped or taken up as whole dollars in order to avoid such an increase or decrease. If in such cases it is necessary to drop fractional parts of a dollar amounting to 50 cents or more, the lower fractions shall be dropped, and if it is necessary to take up as whole dollars fractional parts less than 50 cents, the larger fractions shall be taken. In the case of two equal fractions, the one subject to the lower rate of duty shall be dropped or taken up, as the case may be. In determining a rate of duty dependent upon value, fractional parts of a dollar shall be considered.
(b) Quantities subject to specific duty. Except in the case of alcoholic beverages treated under § 159.4, if a rate of duty is specific and $1 or less per unit, fractional quantities, if less than one-half, shall be disregarded, and if one-half or more shall be treated as a whole unit. Subject to the same exception, if a specific rate is more than $1 per unit, duty shall be assessed upon the exact quantity with any fractional part expressed in the form of a decimal extended to two places.
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