Looks like the Unicode Chart for Bengali does not contain the symbol for Bengali 8 annas (half a rupee).
The following 3 in this particular series for currency calculation are however available:
4 anna (quarter rupee) = U09F7 (Described as “BENGALI CURRENCY NUMERATOR FOUR”)
12 anna (three quarter of a rupee) = U09F8 (Described as “BENGALI CURRENCY NUMERATOR ONE LESS THAN THE DENOMINATOR”)
16 anna (one rupee) = U09F9 (Described as “BENGALI CURRENCY DENOMINATOR”)
Could someone perhaps please validate if this is indeed the case.