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 $227.78   9.357%   $249.0934   $249.09   $249.10   $249.10  
  Purchase #2 $51.70   8.852%   $56.2765   $56.28   $56.30   $56.30  
  Purchase #3 $57.99   3.545%   $60.0457   $60.05   $60.05   $60.00  
  Purchase #4 $213.32   6.160%   $226.4605   $226.46   $226.45   $226.50  
  Purchase #5 $141.92   6.821%   $151.6004   $151.60   $151.60   $151.60  
  Purchase #6 $45.91   3.243%   $47.3989   $47.40   $47.40   $47.40  
  Purchase #7 $149.34   8.457%   $161.9697   $161.97   $161.95   $162.00  
  7 purchase totals = $887.96       $952.8451   $952.85   $952.85   $952.90