You might want to go back and re-read tht section in Hebrews - it's contrasting the Levites and Melchizedek, not Jesus. Melchizedek received tihes from Abraham (and by extension, from Levi through Abraham, "for he was still in the loins of his father when Melchizedek met him. (v. 10)" NKJV Therefore the priesthood of Melchizedek was superior to that of the Levites, and Jesus is a "priest forever according to the order of Melchizedek." (Heb 7:17, Psalm 110:4)
It is a major reach to say this says anything about tithing in NT times.
Shoot, man, I got one of those old Bibles that has Hebrews in the New Testament.
Heb. 7:8. And here men that die receive tithes; but there he receiveth them, of whom it is witnessed that he liveth.
Who is he that Paul or whomever is speaking of!?? Melchizedek? Abraham? Levi? They were alive when Paul or whomever wrote Hebrews???? The tense used is present, not past tense. Therefore, this author was not talking about the Melchizedek/Abram [Abraham] event in Gen.14 in this one verse.
So keep your tithes,cuz the blessings that should have come to you will come our way [Eccl. 2:26].