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 $54.55   13.677%   $62.0108   $62.01   $62.00   $62.00  
  Purchase #2 $61.80   10.449%   $68.2575   $68.26   $68.25   $68.30  
  Purchase #3 $189.43   4.497%   $197.9487   $197.95   $197.95   $197.90  
  Purchase #4 $142.58   12.752%   $160.7618   $160.76   $160.75   $160.80  
  Purchase #5 $214.62   13.189%   $242.9262   $242.93   $242.95   $242.90  
  Purchase #6 $9.66   8.136%   $10.4459   $10.45   $10.45   $10.40  
  Purchase #7 $178.59   5.820%   $188.9839   $188.98   $189.00   $189.00  
  7 purchase totals = $851.23       $931.3348   $931.34   $931.35   $931.30