There is a lot of money in bank accounts and a lot of money is shifted between accounts by big business. The big money will then finally have to pay its share of the tax bill. Tax also becomes much simpler for individuals and small business to work out, setting people free of being the governments unpaid tax inspectors. No more working out your taxes till 2am. Nor having to worry that you've made a mistake. Nor the annual fear of getting tax returns done. It's simply done. Business will no longer have to pay accountants to do the governments taxes for them either, and the accountants will then be able to get on with the job of looking after the business.
And the tax department would disappear, and so would annual budgets as the money would be pouring in all the time.
All salaries paid and all large cash transactions must be done through the banks and all money in banks must be declared so this law does not introduce any new invasions of privacy. And being so simple it provides no loop holes to allow large companies to avoid tax, other than leaving money in the bank which would result in banks having greater liquid assets.
And less money would be inclined to leave the country. Foreign companies would leave their profits in the countries they're made in and use that money for future expansions and investments.
The cash economy is effectively legalised by this tax as it specifically targets only money in the bank. So then small jobs can be done by casual workers who, paid by cash in hand, can then either bank their money or spend it where it goes straight back into the accounted and taxed economic system. Leave the casual workers, and small money will quickly go round the community so it most effectively lubricates the economy.