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 $25.69   3.443%   $26.5745   $26.57   $26.55   $26.60  
  Purchase #2 $133.66   12.422%   $150.2632   $150.26   $150.25   $150.30  
  Purchase #3 $59.32   11.213%   $65.9716   $65.97   $65.95   $66.00  
  Purchase #4 $43.44   8.848%   $47.2836   $47.28   $47.30   $47.30  
  Purchase #5 $150.77   11.304%   $167.813   $167.81   $167.80   $167.80  
  Purchase #6 $249.43   9.157%   $272.2703   $272.27   $272.25   $272.30  
  Purchase #7 $165.62   11.754%   $185.087   $185.09   $185.10   $185.10  
  7 purchase totals = $827.93       $915.2632   $915.25   $915.20   $915.40