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 $151.88   5.737%   $160.5934   $160.59   $160.60   $160.60  
  Purchase #2 $248.97   8.417%   $269.9258   $269.93   $269.95   $269.90  
  Purchase #3 $135.87   13.231%   $153.847   $153.85   $153.85   $153.80  
  Purchase #4 $55.88   6.219%   $59.3552   $59.36   $59.35   $59.40  
  Purchase #5 $10.71   7.481%   $11.5112   $11.51   $11.50   $11.50  
  Purchase #6 $61.25   13.582%   $69.569   $69.57   $69.55   $69.60  
  Purchase #7 $250.80   4.462%   $261.9907   $261.99   $262.00   $262.00  
  7 purchase totals = $915.36       $986.7923   $986.80   $986.80   $986.80