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 $248.53   9.438%   $271.9863   $271.99   $272.00   $272.00  
  Purchase #2 $173.90   13.366%   $197.1435   $197.14   $197.15   $197.10  
  Purchase #3 $90.54   7.724%   $97.5333   $97.53   $97.55   $97.50  
  Purchase #4 $52.34   13.235%   $59.2672   $59.27   $59.25   $59.30  
  Purchase #5 $182.48   7.767%   $196.6532   $196.65   $196.65   $196.70  
  Purchase #6 $60.38   5.121%   $63.4721   $63.47   $63.45   $63.50  
  Purchase #7 $13.73   8.492%   $14.896   $14.90   $14.90   $14.90  
  7 purchase totals = $821.90       $900.9516   $900.95   $900.95   $901.00