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 $114.33   11.591%   $127.582   $127.58   $127.60   $127.60  
  Purchase #2 $94.69   3.210%   $97.7295   $97.73   $97.75   $97.70  
  Purchase #3 $190.84   11.578%   $212.9355   $212.94   $212.95   $212.90  
  Purchase #4 $149.69   11.235%   $166.5077   $166.51   $166.50   $166.50  
  Purchase #5 $53.61   8.792%   $58.3234   $58.32   $58.30   $58.30  
  Purchase #6 $138.99   7.129%   $148.8986   $148.90   $148.90   $148.90  
  Purchase #7 $24.76   3.383%   $25.5976   $25.60   $25.60   $25.60  
  7 purchase totals = $766.91       $837.5743   $837.58   $837.60   $837.50