26 U.S.C. § 6102: Computations on returns or other documents

(a) Amounts shown on internal revenue formsThe Secretary is authorized to provide with respect to any amount required to be shown on a form prescribed for any internal revenue return, statement, or other document, that if such amount of such item is other than a whole-dollar amount, either—(1) the fractional part of a dollar shall be disregarded; or (2) the fractional part of a dollar shall be disregarded unless it amounts to one-half dollar or more, in which case the amount (determined without regard to the fractional part of a dollar) shall be increased by $1. (b) Election not to use whole dollar amountsAny person making a return, statement, or other document shall be allowed, under regulations prescribed by the Secretary, to make such return, statement, or other document without regard to subsection (a). (c) Inapplicability to computation of amountThe provisions of subsections (a) and (b) shall not be applicable to items which must be taken into account in making the computations necessary to determine the amount required to be shown on a form, but shall be applicable only to such final amount.