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 $204.69   11.504%   $228.2375   $228.24   $228.25   $228.20  
  Purchase #2 $41.96   11.484%   $46.7787   $46.78   $46.80   $46.80  
  Purchase #3 $246.45   6.181%   $261.6831   $261.68   $261.70   $261.70  
  Purchase #4 $52.31   5.811%   $55.3497   $55.35   $55.35   $55.30  
  Purchase #5 $59.45   9.265%   $64.958   $64.96   $64.95   $65.00  
  Purchase #6 $212.33   5.614%   $224.2502   $224.25   $224.25   $224.30  
  Purchase #7 $66.94   11.154%   $74.4065   $74.41   $74.40   $74.40  
  7 purchase totals = $884.13       $955.6637   $955.67   $955.70   $955.70