Vekneswaran Sekaran and Saravanak Kumar Karunanithy, both 30, were each sentenced to seven years in jail and 12 strokes of the cane, while 32-year-old Selvam Karupaya was jailed for five years and nine months and 12 strokes of the cane, Channel News Asia reported.
The trio were part of a nine-member gang who had planned the heist months in advance, secretly tailing the money changer to learn his routine, including when he would pick up suitcases full of cash from couriers.
They also staked out his home to familiarise themselves with the surroundings and rehearsed the robbery.
After four aborted attempts in October 2014, the robbers made off with SGD 624,036 in cash after ambushing the victim, Ali Yousof Saiboo, 35, on November 5 that year.
The robbers used a crowbar to smash the windows of Ali's vehicle, dragged him out and snatched his suitcases. One of the robbers threatened to kill Ali's two-year-old son, who was sitting in the front passenger seat.
Deputy Public Prosecutor Michelle Lu said the level of planning that went into the robbery was "unprecedented". The robbers had even stuck plasters on their fingers to avoid leaving any fingerprints at the scene. All of them fled to Malaysia within two hours of the robbery.
Another three of the nine robbers - Malaysian men of Indian origins and aged between 29 and 35 - remain at large.
The first three to be dealt with were sentenced last year to between seven and nine years' jail and 12 strokes of the cane.
The punishment for gang robbery in Singapore is five to 20 years in jail and at least 12 strokes of the cane.