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 $249.55   4.699%   $261.2764   $261.28   $261.30   $261.30  
  Purchase #2 $232.61   11.842%   $260.1557   $260.16   $260.15   $260.20  
  Purchase #3 $205.48   5.711%   $217.215   $217.22   $217.20   $217.20  
  Purchase #4 $63.76   9.795%   $70.0053   $70.01   $70.00   $70.00  
  Purchase #5 $48.46   13.849%   $55.1712   $55.17   $55.15   $55.20  
  Purchase #6 $46.67   6.379%   $49.6471   $49.65   $49.65   $49.60  
  Purchase #7 $90.41   11.463%   $100.7737   $100.77   $100.75   $100.80  
  7 purchase totals = $936.94       $1,014.2444   $1,014.26   $1,014.20   $1,014.30