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 $83.76   11.630%   $93.5013   $93.50   $93.50   $93.50  
  Purchase #2 $9.28   6.301%   $9.8647   $9.86   $9.85   $9.90  
  Purchase #3 $116.46   7.868%   $125.6231   $125.62   $125.60   $125.60  
  Purchase #4 $121.49   7.758%   $130.9152   $130.92   $130.90   $130.90  
  Purchase #5 $247.25   5.556%   $260.9872   $260.99   $261.00   $261.00  
  Purchase #6 $236.42   5.405%   $249.1985   $249.20   $249.20   $249.20  
  Purchase #7 $63.30   9.202%   $69.1249   $69.12   $69.10   $69.10  
  7 purchase totals = $877.96       $939.2149   $939.21   $939.15   $939.20