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 $241.77   8.151%   $261.4767   $261.48   $261.50   $261.50  
  Purchase #2 $197.86   11.338%   $220.2934   $220.29   $220.30   $220.30  
  Purchase #3 $137.96   10.733%   $152.7672   $152.77   $152.75   $152.80  
  Purchase #4 $188.61   9.504%   $206.5355   $206.54   $206.55   $206.50  
  Purchase #5 $205.68   10.542%   $227.3628   $227.36   $227.35   $227.40  
  Purchase #6 $59.38   3.538%   $61.4809   $61.48   $61.50   $61.50  
  Purchase #7 $245.53   7.853%   $264.8115   $264.81   $264.80   $264.80  
  7 purchase totals = $1,276.79       $1,394.7280   $1,394.73   $1,394.75   $1,394.80