Exodus 30:13
This they shall give, every one that passeth among them that are numbered, half a shekel after the shekel of the sanctuary: (a shekel is twenty gerahs:) an half shekel shall be the offering of the LORD. This they shall give, every one that passeth among them that are numbered, half a shekel after the shekel of the sanctuary: (a shekel is twenty gerahs:) an half shekel shall be the offering of the LORD.
Every one who passed among those numbered was required to give a half shekel as the offering of the Lord, a ransom for the soul, and this was in addition to the tithe. The half shekel was to be paid yearly. In Nehemiah's time a yearly contribution for this purpose was made. The money thus collected was used for the service and support of the tabernacle and temple, meeting sanctuary expenses including necessary repairs.
Only the shekel of the sanctuary, called the temple shekel, was accepted for the service of the sanctuary. Jews coming from all parts of Palestine and from distant lands brought foreign coin and had to have it changed for that coin. This required money-changing gave opportunity for fraud and extortion. It grew into a disgraceful traffic that became a source of revenue to the priests.