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 $208.47   13.513%   $236.6406   $236.64   $236.65   $236.60  
  Purchase #2 $134.38   13.618%   $152.6799   $152.68   $152.70   $152.70  
  Purchase #3 $68.58   4.341%   $71.5571   $71.56   $71.55   $71.60  
  Purchase #4 $10.77   8.782%   $11.7158   $11.72   $11.70   $11.70  
  Purchase #5 $60.85   10.535%   $67.2605   $67.26   $67.25   $67.30  
  Purchase #6 $77.83   9.161%   $84.96   $84.96   $84.95   $85.00  
  Purchase #7 $192.44   3.703%   $199.5661   $199.57   $199.55   $199.60  
  7 purchase totals = $753.32       $824.3800   $824.39   $824.35   $824.50