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 $62.41   13.489%   $70.8285   $70.83   $70.85   $70.80  
  Purchase #2 $245.37   8.874%   $267.1441   $267.14   $267.15   $267.10  
  Purchase #3 $229.28   4.416%   $239.405   $239.41   $239.40   $239.40  
  Purchase #4 $197.61   5.256%   $207.9964   $208.00   $208.00   $208.00  
  Purchase #5 $114.92   13.648%   $130.6043   $130.60   $130.60   $130.60  
  Purchase #6 $95.74   4.738%   $100.2762   $100.28   $100.30   $100.30  
  Purchase #7 $231.31   9.602%   $253.5204   $253.52   $253.50   $253.50  
  7 purchase totals = $1,176.64       $1,269.7749   $1,269.78   $1,269.80   $1,269.70