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 $227.82   5.362%   $240.0357   $240.04   $240.05   $240.00  
  Purchase #2 $97.67   4.312%   $101.8815   $101.88   $101.90   $101.90  
  Purchase #3 $249.88   4.271%   $260.5524   $260.55   $260.55   $260.60  
  Purchase #4 $209.90   12.662%   $236.4775   $236.48   $236.50   $236.50  
  Purchase #5 $11.78   11.806%   $13.1707   $13.17   $13.15   $13.20  
  Purchase #6 $40.83   13.749%   $46.4437   $46.44   $46.45   $46.40  
  Purchase #7 $98.67   8.164%   $106.7254   $106.73   $106.75   $106.70  
  7 purchase totals = $936.55       $1,005.2869   $1,005.29   $1,005.35   $1,005.30