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 $62.77   9.546%   $68.762   $68.76   $68.75   $68.80  
  Purchase #2 $51.64   5.754%   $54.6114   $54.61   $54.60   $54.60  
  Purchase #3 $42.87   6.216%   $45.5348   $45.53   $45.55   $45.50  
  Purchase #4 $215.28   7.350%   $231.1031   $231.10   $231.10   $231.10  
  Purchase #5 $182.38   8.214%   $197.3607   $197.36   $197.35   $197.40  
  Purchase #6 $171.86   6.747%   $183.4554   $183.46   $183.45   $183.50  
  Purchase #7 $46.99   8.353%   $50.9151   $50.92   $50.90   $50.90  
  7 purchase totals = $773.79       $831.7425   $831.74   $831.70   $831.80