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 $233.77   12.683%   $263.419   $263.42   $263.40   $263.40  
  Purchase #2 $236.44   12.803%   $266.7114   $266.71   $266.70   $266.70  
  Purchase #3 $67.37   8.868%   $73.3444   $73.34   $73.35   $73.30  
  Purchase #4 $15.30   10.132%   $16.8502   $16.85   $16.85   $16.90  
  Purchase #5 $119.25   5.330%   $125.606   $125.61   $125.60   $125.60  
  Purchase #6 $218.32   8.632%   $237.1654   $237.17   $237.15   $237.20  
  Purchase #7 $200.42   12.395%   $225.2621   $225.26   $225.25   $225.30  
  7 purchase totals = $1,090.87       $1,208.3585   $1,208.36   $1,208.30   $1,208.40