In the case of currency, money was already used way back even before Abraham, under the law, and to date yet, the instruction was specific in Lev 27:30 that, should one give a tithe that comes from the land, the option was whether the (1) seed of the land or (2) fruit of the tree and, should one give livestock, the 10th that passes the rod was the tithe (Lev 27:32)
In short, money was not in the option. In fact, if the place of worship was too far (Deut 14:24-26), it can be exchanged with money (proving that money was already in used) but, should they reach the place of worship, they would spend it buying foods and not directly given in the currency of money.
Should the Pastors said that they were mostly farmers at that time, well, I beg to differ, Pharisee in Matt 23:23 were not farmers yet, they gave in anis, Cummins, etc.
Matt 22: 21-22 is typically used to prove that we should render to Ceasar what is Ceasar’s and render to God what is of God.
But, if you read it from verse 18 to 22 when Jesus was tested, He asked first for the money and asked, Whose image and inscription is this? When they said, Ceasar’s, he responded saying, Render therefore to Caesar the things that are Caesar’s.
Here, Jesus clearly identifies that money was of Ceasar’s yet, what is of Ceasar’s is also given to God? Should this be the case, Jesus distinguishing that money was of Ceasar’s became pointless since it is also being given now as a currency of tithe.
In actuality, the tithe which is of God was not really given in the currency of money but in the currency of agriculture and livestock since God’s inscription is on those.
Although the raw material of Money came from God, the finished product which is money is of Man, while agricultural and animals are of God.
The above is the requirement of WHAT to tithe.
In today’s time, however it may seem inconvenient, the above is still doable. But, the second requirement which is according to Num 18:21, Nehemiah 10:38 was to be received by Levites is now impossible to do because, in Heb 7:12, they were change and so, even if we used the concept of parallelism, should a pastor parallel themselves to Levites nowadays, they would just parallel themselves to someone who already loses the rights to collect it since tithe was given to Levites in connection to their priestly obligation.