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Sales Tax: Rounded Then Totaled or Totaled Then Rounded?
You should total the items first, to get $3.00, then add the tax, then round up/down accordingly.  Your two examples above don't offer this option, even though your second example arrives at the same result.  In your first example, a number of items taxed one at a time might result in many .006 results which would round to .01. A long enough list of items would result in an error of many cents depending how many items there are. Totaling first then applying tax results in your saving .004 or losing .005 cents maximum due to rounding.  See A Guide to Sales and Use Tax which is a document put out by the Massachusetts Dept of Revenue. In the chart for tax, it shows that $1.09 is taxed at five cents, but at 5%, it would be 5.45. So, at least for this state, I believe I correctly stated the rounding process.