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 $237.89   9.198%   $259.7711   $259.77   $259.75   $259.80  
  Purchase #2 $60.68   4.815%   $63.6017   $63.60   $63.60   $63.60  
  Purchase #3 $126.28   4.790%   $132.3288   $132.33   $132.35   $132.30  
  Purchase #4 $75.25   3.855%   $78.1509   $78.15   $78.15   $78.20  
  Purchase #5 $171.98   12.701%   $193.8232   $193.82   $193.80   $193.80  
  Purchase #6 $30.68   13.797%   $34.9129   $34.91   $34.90   $34.90  
  Purchase #7 $244.74   6.679%   $261.0862   $261.09   $261.10   $261.10  
  7 purchase totals = $947.50       $1,023.6748   $1,023.67   $1,023.65   $1,023.70