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 $52.74   12.118%   $59.131   $59.13   $59.15   $59.10  
  Purchase #2 $64.99   4.136%   $67.678   $67.68   $67.70   $67.70  
  Purchase #3 $108.43   5.827%   $114.7482   $114.75   $114.75   $114.70  
  Purchase #4 $98.44   6.523%   $104.8612   $104.86   $104.85   $104.90  
  Purchase #5 $77.60   8.703%   $84.3535   $84.35   $84.35   $84.40  
  Purchase #6 $132.55   10.621%   $146.6281   $146.63   $146.65   $146.60  
  Purchase #7 $148.40   6.488%   $158.0282   $158.03   $158.05   $158.00  
  7 purchase totals = $683.15       $735.4282   $735.43   $735.50   $735.40