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 $63.93   13.197%   $72.3668   $72.37   $72.35   $72.40  
  Purchase #2 $13.73   3.779%   $14.2489   $14.25   $14.25   $14.20  
  Purchase #3 $168.42   5.730%   $178.0705   $178.07   $178.05   $178.10  
  Purchase #4 $250.27   4.366%   $261.1968   $261.20   $261.20   $261.20  
  Purchase #5 $130.39   6.683%   $139.104   $139.10   $139.10   $139.10  
  Purchase #6 $69.97   6.653%   $74.6251   $74.63   $74.65   $74.60  
  Purchase #7 $77.26   6.850%   $82.5523   $82.55   $82.55   $82.60  
  7 purchase totals = $773.97       $822.1644   $822.17   $822.15   $822.20