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 $58.93   13.704%   $67.0058   $67.01   $67.00   $67.00  
  Purchase #2 $203.84   13.757%   $231.8823   $231.88   $231.90   $231.90  
  Purchase #3 $190.71   8.195%   $206.3387   $206.34   $206.35   $206.30  
  Purchase #4 $24.97   5.495%   $26.3421   $26.34   $26.35   $26.30  
  Purchase #5 $57.81   3.709%   $59.9542   $59.95   $59.95   $60.00  
  Purchase #6 $128.89   13.304%   $146.0375   $146.04   $146.05   $146.00  
  Purchase #7 $200.69   8.281%   $217.3091   $217.31   $217.30   $217.30  
  7 purchase totals = $865.84       $954.8697   $954.87   $954.90   $954.80