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 $250.83   4.517%   $262.16   $262.16   $262.15   $262.20  
  Purchase #2 $136.68   9.486%   $149.6455   $149.65   $149.65   $149.60  
  Purchase #3 $43.32   13.703%   $49.2561   $49.26   $49.25   $49.30  
  Purchase #4 $25.54   3.481%   $26.429   $26.43   $26.45   $26.40  
  Purchase #5 $101.87   12.339%   $114.4397   $114.44   $114.45   $114.40  
  Purchase #6 $119.45   13.147%   $135.1541   $135.15   $135.15   $135.20  
  Purchase #7 $167.75   6.407%   $178.4977   $178.50   $178.50   $178.50  
  7 purchase totals = $845.44       $915.5821   $915.59   $915.60   $915.60