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 $56.59   11.382%   $63.0311   $63.03   $63.05   $63.00  
  Purchase #2 $121.55   9.110%   $132.6232   $132.62   $132.60   $132.60  
  Purchase #3 $15.83   11.146%   $17.5944   $17.59   $17.60   $17.60  
  Purchase #4 $181.58   3.785%   $188.4528   $188.45   $188.45   $188.50  
  Purchase #5 $179.31   10.630%   $198.3707   $198.37   $198.35   $198.40  
  Purchase #6 $42.95   10.193%   $47.3279   $47.33   $47.35   $47.30  
  Purchase #7 $191.87   8.770%   $208.697   $208.70   $208.70   $208.70  
  7 purchase totals = $789.68       $856.0971   $856.09   $856.10   $856.10