The price of goods, especially food, won't go up 40%
Data show that sales taxes can't realistically increase beyond 13%. Up to that point while black markets are a nuisance they aren't a major problem. Beyond 13% sales tax black markets an other non-taxed trading do overwhelm the system. Net income tax revenues rarely exceed 23% regardless of how high any marginal rate of income tax is. In fact, the only way found so far to support the 40%+ tax rates of most European countries is the VAT.
This question is much debated in the US, and I am firmly of the belief that the best way to protect everyone's interests is a flat income tax. I'd make an exclusion at the level below which it would cost the government more to process the tax claim than they receive in taxes. I understand the economic engine aspects of the fair or highish flat sales tax. But I believe there is a more important moral question that can only be addressed by the income tax. Right now there is too much greed and ency in the system masquerading as "fairness." These evils will only fade when the poor man's money is as much at risk as the rich man's money.