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 $66.60   4.149%   $69.3632   $69.36   $69.35   $69.40  
  Purchase #2 $104.41   9.609%   $114.4428   $114.44   $114.45   $114.40  
  Purchase #3 $208.69   13.691%   $237.2617   $237.26   $237.25   $237.30  
  Purchase #4 $205.66   5.687%   $217.3559   $217.36   $217.35   $217.40  
  Purchase #5 $53.77   9.360%   $58.8029   $58.80   $58.80   $58.80  
  Purchase #6 $113.39   12.359%   $127.4039   $127.40   $127.40   $127.40  
  Purchase #7 $175.33   12.120%   $196.58   $196.58   $196.60   $196.60  
  7 purchase totals = $927.85       $1,021.2104   $1,021.20   $1,021.20   $1,021.30