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 $236.69   10.674%   $261.9543   $261.95   $261.95   $262.00  
  Purchase #2 $96.57   8.290%   $104.5757   $104.58   $104.60   $104.60  
  Purchase #3 $171.48   6.719%   $183.0017   $183.00   $183.00   $183.00  
  Purchase #4 $65.93   3.563%   $68.2791   $68.28   $68.30   $68.30  
  Purchase #5 $143.56   5.594%   $151.5907   $151.59   $151.60   $151.60  
  Purchase #6 $61.80   5.816%   $65.3943   $65.39   $65.40   $65.40  
  Purchase #7 $146.56   5.631%   $154.8128   $154.81   $154.80   $154.80  
  7 purchase totals = $922.59       $989.6086   $989.60   $989.65   $989.70