All four of Australia's big banks now own cash logistics provider Cash Services Australia, with National Australia Bank (NAB) on Thursday taking a 25 per cent stake in the business. The Commonwealth Bank of Australia (CBA), Westpac and ANZ already have stakes in Cash Services Australia. The development is part of an industry-wide trend to outsource some back-office functions, with NAB, Westpac and CBA joining together earlier this year to have their cheque-processing functions performed by specialist technology provider Fiserv.