Exodus 30:12
When thou takest the sum of the children of Israel after their number, then shall they give every man a ransom for his soul unto the LORD, when thou numberest them; that there be no plague among them, when thou numberest them. When thou takest the sum of the children of Israel after their number, then shall they give every man a ransom for his soul unto the LORD, when thou numberest them; that there be no plague among them, when thou numberest them.
Every Israelite was required to give a half shekel as the ransom price for his life. The payment was due yearly. It was due whenever the people were numbered. The money collected was to support the service and upkeep of the tabernacle, and in later times the temple.
In later times the tax was paid at Jerusalem at Passover by crowds gathered from all parts of Palestine and distant lands. Large sums were also brought at that time as freewill offerings for the temple treasury. Only the temple shekel was accepted for sanctuary service, so all foreign coin had to be exchanged into it. That money-changing business became a system of fraud and extortion and a source of revenue for the priests.