Charles Ellicott Commentary Leviticus 27:31

"And if a man will redeem aught of his tithe, he shall add unto it the fifth part thereof." — Leviticus 27:31 (ASV)

And if a man will at all redeem. —Better And if a man wishes to redeem. (Leviticus 27:19) Though a man may not vow tithes, since they are already the Lord’s, yet if he wishes, he may redeem them by adding one-fifth to their actual value.

According to the authorities during the Second Temple period, anyone was allowed to redeem the tithes due from another person by paying their exact value, without the addition of the fifth part. The tithes could then be eaten in any place, but the redemption money had to be taken to Jerusalem, where it was spent in sociable feasts to which the Levite, the stranger, and the poor were invited.