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 $154.97   7.801%   $167.0592   $167.06   $167.05   $167.10  
  Purchase #2 $224.31   4.745%   $234.9535   $234.95   $234.95   $235.00  
  Purchase #3 $118.77   10.620%   $131.3834   $131.38   $131.40   $131.40  
  Purchase #4 $19.87   8.158%   $21.491   $21.49   $21.50   $21.50  
  Purchase #5 $25.97   9.744%   $28.5005   $28.50   $28.50   $28.50  
  Purchase #6 $221.95   5.636%   $234.4591   $234.46   $234.45   $234.50  
  Purchase #7 $130.66   7.341%   $140.2518   $140.25   $140.25   $140.30  
  7 purchase totals = $896.50       $958.0985   $958.09   $958.10   $958.30