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 $59.95   10.713%   $66.3724   $66.37   $66.35   $66.40  
  Purchase #2 $210.97   13.648%   $239.7632   $239.76   $239.75   $239.80  
  Purchase #3 $72.58   9.224%   $79.2748   $79.27   $79.25   $79.30  
  Purchase #4 $215.81   12.271%   $242.292   $242.29   $242.30   $242.30  
  Purchase #5 $249.90   4.691%   $261.6228   $261.62   $261.60   $261.60  
  Purchase #6 $135.82   3.755%   $140.92   $140.92   $140.90   $140.90  
  Purchase #7 $142.77   6.712%   $152.3527   $152.35   $152.35   $152.40  
  7 purchase totals = $1,087.80       $1,182.5979   $1,182.58   $1,182.50   $1,182.70