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 $73.26   12.552%   $82.4556   $82.46   $82.45   $82.50  
  Purchase #2 $129.36   10.688%   $143.186   $143.19   $143.20   $143.20  
  Purchase #3 $87.50   12.533%   $98.4664   $98.47   $98.45   $98.50  
  Purchase #4 $242.35   7.688%   $260.9819   $260.98   $261.00   $261.00  
  Purchase #5 $171.76   12.179%   $192.6787   $192.68   $192.70   $192.70  
  Purchase #6 $190.42   8.715%   $207.0151   $207.02   $207.00   $207.00  
  Purchase #7 $237.29   5.337%   $249.9542   $249.95   $249.95   $250.00  
  7 purchase totals = $1,131.94       $1,234.7379   $1,234.75   $1,234.75   $1,234.90