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:
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