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 $249.95   9.758%   $274.3401   $274.34   $274.35   $274.30  
  Purchase #2 $21.39   5.213%   $22.5051   $22.51   $22.50   $22.50  
  Purchase #3 $91.84   5.602%   $96.9849   $96.98   $97.00   $97.00  
  Purchase #4 $6.59   9.178%   $7.1948   $7.19   $7.20   $7.20  
  Purchase #5 $214.84   3.754%   $222.9051   $222.91   $222.90   $222.90  
  Purchase #6 $154.75   10.765%   $171.4088   $171.41   $171.40   $171.40  
  Purchase #7 $208.59   4.370%   $217.7054   $217.71   $217.70   $217.70  
  7 purchase totals = $947.95       $1,013.0442   $1,013.05   $1,013.05   $1,013.00