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 $250.53   12.677%   $282.2897   $282.29   $282.30   $282.30  
  Purchase #2 $53.34   9.814%   $58.5748   $58.57   $58.55   $58.60  
  Purchase #3 $72.62   3.203%   $74.946   $74.95   $74.95   $74.90  
  Purchase #4 $12.70   10.783%   $14.0694   $14.07   $14.05   $14.10  
  Purchase #5 $97.98   4.379%   $102.2705   $102.27   $102.25   $102.30  
  Purchase #6 $244.76   6.351%   $260.3047   $260.30   $260.30   $260.30  
  Purchase #7 $128.98   5.509%   $136.0855   $136.09   $136.10   $136.10  
  7 purchase totals = $860.91       $928.5406   $928.54   $928.50   $928.60