Which country use tax brackets as part of their tax system?

After the 2008 recession, the amount of reserves in the us banking system increased. because of federal reserve actions, required reserves increased from $44 billion to $60 billion. however, banks started holding more reserves than required. by january 2009, banks were holding $900 billion in excess reserves. the federal reserve started paying interest on the excess reserves that the banks held. what possible impact will these unused reserves have on the economy?