CoStar Group Inc. sweetened its offer for Domain Holdings Australia Ltd. by 5.5% to A$2.8 billion ($1.8 billion), a big enough bump to persuade the Australian property portal to open up its books.

Domain to support deal, pending superior offers and expert approval CoStar's final offer at A$4.43/share Domain down 2.3% Shares of Domain slipped as much as 2.3% to A$4.230, as of 0218 GMT. Sign ...