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 $73.67   11.543%   $82.1737   $82.17   $82.15   $82.20  
  Purchase #2 $187.86   13.857%   $213.8918   $213.89   $213.90   $213.90  
  Purchase #3 $240.70   8.579%   $261.3497   $261.35   $261.35   $261.30  
  Purchase #4 $232.70   7.661%   $250.5271   $250.53   $250.55   $250.50  
  Purchase #5 $119.60   11.610%   $133.4856   $133.49   $133.50   $133.50  
  Purchase #6 $93.65   5.350%   $98.6603   $98.66   $98.65   $98.70  
  Purchase #7 $9.59   10.728%   $10.6188   $10.62   $10.60   $10.60  
  7 purchase totals = $957.77       $1,050.7070   $1,050.71   $1,050.70   $1,050.70