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 $218.28   11.659%   $243.7293   $243.73   $243.75   $243.70  
  Purchase #2 $208.69   4.698%   $218.4943   $218.49   $218.50   $218.50  
  Purchase #3 $115.89   5.425%   $122.177   $122.18   $122.20   $122.20  
  Purchase #4 $54.60   3.867%   $56.7114   $56.71   $56.70   $56.70  
  Purchase #5 $249.65   6.623%   $266.1843   $266.18   $266.20   $266.20  
  Purchase #6 $128.34   10.370%   $141.6489   $141.65   $141.65   $141.60  
  Purchase #7 $217.92   8.831%   $237.1645   $237.16   $237.15   $237.20  
  7 purchase totals = $1,193.37       $1,286.1097   $1,286.10   $1,286.15   $1,286.10