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 $247.91   6.206%   $263.2953   $263.30   $263.30   $263.30  
  Purchase #2 $227.41   10.195%   $250.5944   $250.59   $250.60   $250.60  
  Purchase #3 $71.38   13.715%   $81.1698   $81.17   $81.15   $81.20  
  Purchase #4 $64.32   5.857%   $68.0872   $68.09   $68.10   $68.10  
  Purchase #5 $223.57   8.361%   $242.2627   $242.26   $242.25   $242.30  
  Purchase #6 $16.44   9.788%   $18.0491   $18.05   $18.05   $18.00  
  Purchase #7 $32.60   7.402%   $35.0131   $35.01   $35.00   $35.00  
  7 purchase totals = $883.63       $958.4716   $958.47   $958.45   $958.50