>That depends on the context. If the context is currency, you will mostly only consider two decimals
>
>In your tax problem
>
>

>base for federal tax = 500.00
>round(500.00 * .05, 2) = 25.00 && federal tax
>
>base for  provincial tax = 500.00 + 25.00 = 525.00
>
>round( ( 500.00 + 25.00) * 9.5 / 100, 2) = 49.88 && provincial tax
>
>Total = 500.00 + 25.00 + 49.88 = 574.88
>

>
>So, if you want to reverse the process, you have to apply the steps backwards - one at a time - do not combine them - this is no algebra
>After each division you have to round to 2 decimals
>
>

>Total = 574.88
>(1) 
>Base for provincial tax = round( 574.88 / 1.095, 2) = 525.00
>
>provincial tax = 574.88 -  525.00 = 49.88
>
>(2) 
>base for federal tax = Base for provincial tax / 1.05
>base for federal tax = round( 525.00 / 1.05, 2)  = 500.00
>federal tax = 525.00 - 500.00 = 25.00
>
>

>
>iow, you need two decimals since the taxes were calculated with two decimals
>
>You apply the steps backwards
> - dividing and rounding to 2 decimals to obtain the base
> - subtracting to obtain the tax ( do not use a division here )

Thanks, this sums it all assuming you have the original amount. In the other thread, where I am looking for the formula, we do not have the original amount. We only have the total tax amount and we need to collect each tax from that total tax amount.