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 $243.81   11.241%   $271.2167   $271.22   $271.20   $271.20  
  Purchase #2 $250.38   4.328%   $261.2164   $261.22   $261.20   $261.20  
  Purchase #3 $164.67   13.796%   $187.3879   $187.39   $187.40   $187.40  
  Purchase #4 $35.95   4.307%   $37.4984   $37.50   $37.50   $37.50  
  Purchase #5 $168.29   5.545%   $177.6217   $177.62   $177.60   $177.60  
  Purchase #6 $129.63   6.221%   $137.6943   $137.69   $137.70   $137.70  
  Purchase #7 $153.91   3.680%   $159.5739   $159.57   $159.55   $159.60  
  7 purchase totals = $1,146.64       $1,232.2093   $1,232.21   $1,232.15   $1,232.20