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 $232.74   12.503%   $261.8395   $261.84   $261.85   $261.80  
  Purchase #2 $40.97   8.163%   $44.3144   $44.31   $44.30   $44.30  
  Purchase #3 $5.85   12.393%   $6.575   $6.58   $6.60   $6.60  
  Purchase #4 $81.62   9.271%   $89.187   $89.19   $89.20   $89.20  
  Purchase #5 $124.57   5.268%   $131.1323   $131.13   $131.15   $131.10  
  Purchase #6 $177.62   13.382%   $201.3891   $201.39   $201.40   $201.40  
  Purchase #7 $158.69   3.489%   $164.2267   $164.23   $164.25   $164.20  
  7 purchase totals = $822.06       $898.6640   $898.67   $898.75   $898.60