Your original makes little sense since ob'yekty oblozheniya = baza. So it's either/or, not both. Hence it should be объекты обложения (налоговая база), i.e. you need to scratch the second baza in the original. The Russians are very fond of this nalogovaya baza of theirs, which you can translate as tax base if you absolutely have to even though no one really calls it that, not on our side of the ocean anyway. Speaking of most taxes it's better to call it amounts/revenue/income/whatever subject to tax. In case of customs duties, it is technically speaking goods that are subject to tax rather than monetary amounts even though the duties are more often than not assessed on the value of these goods rather than their physical count. Call it goods subject to customs duty and you'll be all right nine times out of ten.