(a) No registered investment company issuing any redeemable security, no person designated in such issuer's prospectus as authorized to consummate transactions in any such security, and no principal underwriter of, or dealer in, any such security shall sell, redeem, or repurchase any such security except at a price based on the current net asset value of such security which is next computed after receipt of a tender of such security for redemption or of an order to purchase or sell such security: