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 $53.29   6.861%   $56.9462   $56.95   $56.95   $56.90  
  Purchase #2 $180.52   4.180%   $188.0657   $188.07   $188.05   $188.10  
  Purchase #3 $118.70   4.217%   $123.7056   $123.71   $123.70   $123.70  
  Purchase #4 $244.71   6.811%   $261.3772   $261.38   $261.40   $261.40  
  Purchase #5 $12.65   4.395%   $13.206   $13.21   $13.20   $13.20  
  Purchase #6 $46.41   10.491%   $51.2789   $51.28   $51.30   $51.30  
  Purchase #7 $70.78   8.779%   $76.9938   $76.99   $77.00   $77.00  
  7 purchase totals = $727.06       $771.5734   $771.59   $771.60   $771.60