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 $241.74   6.559%   $257.5957   $257.60   $257.60   $257.60  
  Purchase #2 $57.87   11.263%   $64.3879   $64.39   $64.40   $64.40  
  Purchase #3 $84.72   11.351%   $94.3366   $94.34   $94.35   $94.30  
  Purchase #4 $130.60   4.808%   $136.8792   $136.88   $136.90   $136.90  
  Purchase #5 $21.41   12.445%   $24.0745   $24.07   $24.05   $24.10  
  Purchase #6 $245.99   6.179%   $261.1897   $261.19   $261.20   $261.20  
  Purchase #7 $186.98   12.748%   $210.8162   $210.82   $210.80   $210.80  
  7 purchase totals = $969.31       $1,049.2798   $1,049.29   $1,049.30   $1,049.30