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 $241.43   8.457%   $261.8477   $261.85   $261.85   $261.80  
  Purchase #2 $120.71   9.612%   $132.3126   $132.31   $132.30   $132.30  
  Purchase #3 $108.36   5.787%   $114.6308   $114.63   $114.65   $114.60  
  Purchase #4 $51.72   8.134%   $55.9269   $55.93   $55.95   $55.90  
  Purchase #5 $245.97   12.133%   $275.8135   $275.81   $275.80   $275.80  
  Purchase #6 $146.94   9.387%   $160.7333   $160.73   $160.75   $160.70  
  Purchase #7 $47.87   6.647%   $51.0519   $51.05   $51.05   $51.10  
  7 purchase totals = $963.00       $1,052.3167   $1,052.31   $1,052.35   $1,052.20