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 $84.46   11.228%   $93.9432   $93.94   $93.95   $93.90  
  Purchase #2 $203.41   10.249%   $224.2575   $224.26   $224.25   $224.30  
  Purchase #3 $90.35   4.491%   $94.4076   $94.41   $94.40   $94.40  
  Purchase #4 $225.84   10.489%   $249.5284   $249.53   $249.55   $249.50  
  Purchase #5 $239.56   9.328%   $261.9062   $261.91   $261.90   $261.90  
  Purchase #6 $242.63   8.672%   $263.6709   $263.67   $263.65   $263.70  
  Purchase #7 $112.74   11.501%   $125.7062   $125.71   $125.70   $125.70  
  7 purchase totals = $1,198.99       $1,313.4200   $1,313.43   $1,313.40   $1,313.40