The Venezuelan unit of Mexican cement company Cemex (CX) reopened its administrative offices Tuesday after the Seniat tax authority shut them on Monday for bookkeeping irregularities, said a company executive.  "The offices are open," said Corporate Director Luis Manuel de Llano.  He said Vencemos, as Cemex’s local unit is known, plans to pay a $106,000 tax fine shortly. He added that the administrative closure caused no losses, as the company’s plants remained operational Monday. Vencemos’ sales hit $134.7m last year amid robust growth in the construction industry.