GST Tax Calculation

When doing rounding, please take note of the following:

A = price without GST

B = GST

C = price with GST

Formula

A + B = C

Method 1:

A = round ( C * 100 / 106)

B = C - A

Method 2:

B = round ( C * 6/106)

A = C - B

Method 1 will give you more accurate figure. Method 2 will give you bigger rounding error. I know the difference is subtle, but rounding a number gives you higher precision when the number of significant figures are bigger. (Maths and physics in O level / SPM).

For more background reading:

http://en.wikipedia.org/wiki/Significant_figures