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 $110.81   4.260%   $115.5305   $115.53   $115.55   $115.50  
  Purchase #2 $92.72   6.352%   $98.6096   $98.61   $98.60   $98.60  
  Purchase #3 $11.89   12.284%   $13.3506   $13.35   $13.35   $13.40  
  Purchase #4 $66.64   3.389%   $68.8984   $68.90   $68.90   $68.90  
  Purchase #5 $214.63   10.170%   $236.4579   $236.46   $236.45   $236.50  
  Purchase #6 $206.72   9.377%   $226.1041   $226.10   $226.10   $226.10  
  Purchase #7 $118.86   3.804%   $123.3814   $123.38   $123.40   $123.40  
  7 purchase totals = $822.27       $882.3325   $882.33   $882.35   $882.40