D.C. Code § 42-1119

For the purpose of avoiding, in the case of any stamps or devices employed pursuant to authority of this chapter, the issuance of stamps or the employment of devices representing fractional parts of $1, the Mayor is authorized, in his discretion, to limit the denominations of such stamps or devices to amounts representing $1 or multiples of $1, and to prescribe further that where part of the tax due is a fraction of $1, the tax paid shall be paid to the nearest dollar.