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 $241.84   3.393%   $250.0456   $250.05   $250.05   $250.00  
  Purchase #2 $217.98   11.316%   $242.6466   $242.65   $242.65   $242.60  
  Purchase #3 $53.39   3.531%   $55.2752   $55.28   $55.30   $55.30  
  Purchase #4 $179.82   8.779%   $195.6064   $195.61   $195.60   $195.60  
  Purchase #5 $227.83   3.790%   $236.4648   $236.46   $236.45   $236.50  
  Purchase #6 $60.71   12.149%   $68.0857   $68.09   $68.10   $68.10  
  Purchase #7 $92.92   6.214%   $98.694   $98.69   $98.70   $98.70  
  7 purchase totals = $1,074.49       $1,146.8183   $1,146.83   $1,146.85   $1,146.80