27 CFR §41.115

Remittance of the full amount of internal revenue tax computed during the return period shall accompany the return, except as prescribed in § 41.115a. Such remittance may be in any form the appropriate TTB officer is authorized to accept under the provisions of § 70.61 of this chapter (Payment by check or money order) and which is acceptable to that officer. In paying the tax, a fractional part of a cent shall be disregarded unless it amounts to one-half cent or more, in which case it shall be increased to one cent.