Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $61.89   3.524%   $64.071   $64.07   $64.05   $64.10  
  Purchase #2 $55.58   6.199%   $59.0254   $59.03   $59.05   $59.00  
  Purchase #3 $100.62   6.514%   $107.1744   $107.17   $107.15   $107.20  
  Purchase #4 $27.52   12.331%   $30.9135   $30.91   $30.90   $30.90  
  Purchase #5 $186.53   4.150%   $194.271   $194.27   $194.25   $194.30  
  Purchase #6 $214.36   8.719%   $233.05   $233.05   $233.05   $233.10  
  Purchase #7 $217.82   5.216%   $229.1815   $229.18   $229.20   $229.20  
  7 purchase totals = $864.32       $917.6868   $917.68   $917.65   $917.80