A careful study of God's Word will reveal exactly when the New Covenant was instituted. It is clear from Scripture that in order for the Testament or Covenant to begin a death must occur (Hebrews 9). Jesus' birth, therefore, didn't institute the beginning of the New Covenant. Rather it was His death and victorious resurrection.
Therefore, when you search the end of the Gospels and the record of Acts and the Epistles and the Prophetic book of Revelation what is conspicuously missing is the instruction to continue the practice of Tithing. Before one cites Jesus own words about the Tithe, understand He was speaking of matters concerning the Law. Still, others will quickly cite Hebrews 7.