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 $233.76   6.825%   $249.7141   $249.71   $249.70   $249.70  
  Purchase #2 $130.54   4.516%   $136.4352   $136.44   $136.45   $136.40  
  Purchase #3 $42.85   6.692%   $45.7175   $45.72   $45.70   $45.70  
  Purchase #4 $88.58   4.551%   $92.6113   $92.61   $92.60   $92.60  
  Purchase #5 $113.40   9.619%   $124.3079   $124.31   $124.30   $124.30  
  Purchase #6 $126.34   11.232%   $140.5305   $140.53   $140.55   $140.50  
  Purchase #7 $69.53   10.338%   $76.718   $76.72   $76.70   $76.70  
  7 purchase totals = $805.00       $866.0345   $866.04   $866.00   $865.90