Shekalim (שְׁקָלִים) is the fourth tractate in the order of Mo’ed, which deals with the annual half-shekel tax collected for the maintenance of the Temple and its services, and other attending appurtenances. A shekel is a unit of currency, having begun its life as a unit of weight of gold or silver. In the third millennium BCE, for instance, the unit was 8.4 grams in Babylonia. The weights changed through the centuries, and the Phoenicians had a different set of weight measurements from the Babylonians. The value of a modern Israeli shekel today is about 28 cents.
Usually falling right between synagogue dues time and federal tax time, Shabbat Shekalim is the first of four special Shabbatot before Pesah. For the occasion we read as the Maftir Exodus 30:11 et seq. which talks about the assessment of the tax, possibly for just a one-time count of the community (or at least of its men). The tax was later again mentioned in II Kings 12:5-17 and 22:3-7, in II Chronicles 24:5-14 and 34:8-14, and in Nehemiah 10:33-34, and in those references it appears as a permanent practice.
Shabbat Shekalim always falls before or on the first day of Adar, or in a leap year (as this year is) before Adar II. Since we will read three times “mahatsit hashekel” - “מַחֲצִית הַשֶּׁקֶל” - we have developed a common current practice at Purim time of contributing three half-shekels (perhaps $1.50 in the U.S. or Canada). Nowadays we support modern Jewish institutions or causes, as we no longer are supporting the Mishkan or the Temple. Of course, your synagogue is a pretty good place to begin, after Shabbat!
We also will have a special haftarah (2 Kings 12:1-17), which begins with smashing of idols and installing a seven-year-old king Jehoash, and continues with the decreed description of the distribution of funds donated to the House of the Lord to the priests who were entrusted to disburse it accordingly for building maintenance. When King Jehoash was in his 23rd year of reigning, he noticed that the House was not exactly in good repair. The method of collection and disbursement was altered and the condition of the House was ameliorated.
Taxes, census, and disbursement of tax monies…. so little has changed.