BigDecimal

• How to Use Java BigDecimal

Ability to specify a scale, which represents the number of digits after the decimal place
Ability to specify a rounding method
The java.math.BigDecimal class handles both of these considerations.

suppose we have a product which costs 10.00 in a given currency and the local sales tax is 0.0825, or 8.25%. If we work it out on paper, the tax amount is,
10.00 * 0.0825 = 0.825
Because our precision for the currency is two digits after the decimal, we need to round the 0.825 figure. Also, because this is a tax, it is good practice to always round up to the next highest cent. That way when the accounts are balanced at the end of the day, we never find ourselves underpaying taxes.
0.825 -> 0.83
so the total we charge to the customer is 10.83 in the local currency and pay 0.83 to the tax collector. Note that if we sold 1000 of these, we would have overpaid the collector by this much,
1000 * (0.83 - 0.825) = 5.00

http://www.opentaps.org/docs/index.php/How_to_Use_Java_BigDecimal:_A_Tutorial

• The java.math.BigDecimal class provides operations for arithmetic, scale manipulation, rounding, comparison, hashing, and format conversion.

Two types of operations are provided for manipulating the scale of a BigDecimal:

    scaling/rounding operations
    decimal point motion operations.
http://www.tutorialspoint.com/java/math/java_math_bigdecimal.htm