"The more transparent and democratic the elections are, the higher Tajikistan's credibility will be on the world stage."
Rakhmon, who became head of state in 1992, has been criticised by opponents for undermining civil rights, jailing dissidents and allowing only a token opposition.
But his governing People's Democratic Party, which now holds a majority of seats in the lower house of parliament, was expected to emerge victorious, analysts predicted.
Alidzhon Khakimov, a 59-year-old economist, told The Associated Press news agency that he voted for the governing party because he believes it is working to ensure a better future for Tajiks.
"This party is our well-being, our future.
"They have pure intentions, they have a pure heart and people believe in them"
Badriddin Rustamov, a Tajik voter on the opposition
"They are building the Rogun hydroelectric plant for us and will bring us to energy independence," he said, referring to a proposed plant that would allow the country meet its electricity needs and export power to Afghanistan and Pakistan.
But the poll also had the potential to increase the influence of the opposition Islamic Revival party.
Many of those voting in the capital said they backed the Islamic Revival Party, which currently has only two deputies in the 63-seat parliament.
"They have pure intentions, they have a pure heart and people believe in them," Badriddin Rustamov, an engineer, told The AP.
"I don't know the leader of the party, whom I've only seen on television, but I feel that I can trust him and he would do a better job."