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 $59.92   7.116%   $64.1839   $64.18   $64.20   $64.20  
  Purchase #2 $132.43   10.799%   $146.7311   $146.73   $146.75   $146.70  
  Purchase #3 $182.41   3.488%   $188.7725   $188.77   $188.75   $188.80  
  Purchase #4 $110.60   5.430%   $116.6056   $116.61   $116.60   $116.60  
  Purchase #5 $77.80   13.801%   $88.5372   $88.54   $88.55   $88.50  
  Purchase #6 $196.53   4.147%   $204.6801   $204.68   $204.70   $204.70  
  Purchase #7 $47.34   3.627%   $49.057   $49.06   $49.05   $49.10  
  7 purchase totals = $807.03       $858.5674   $858.57   $858.60   $858.60