In the US and indeed around the world, there are very few "tax on taxes" situations. These situations are generally called out where they exist and politicians are pressured to change them; it is generally considered onerous for a government to include an amount of taxes in calculating another tax, because the government is then taxing the money you're already paying them. This is why most U.S. State and local taxes (sales taxes, property taxes, etc) are deductible from your income when itemizing deductions (the alternate "standard deduction" is an "average" amount that a person/household would be able to deduct if they itemized all lower-level taxes they had paid).

So, most taxes, especially sales taxes/duties/tariffs, are all levied on a "pre-tax" or "subtotal" amount. In your example, all three of those taxes would be calculated on the $100 "subtotal" amount, before any other tax is added, and then those amounts are added to the subtotal to produce the grand total (of $147 as Alex shows).

In what order are taxes applied
I managed to set page titles with the "Page Titles" module and keywords and description with the "Meta Tags (Quick)" plugin, however it seems like there is currently no way of having custom keywords/description for the front-page. Does anybody knows of a work around this?
