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 $71.88   6.386%   $76.4703   $76.47   $76.45   $76.50  
  Purchase #2 $203.53   5.509%   $214.7425   $214.74   $214.75   $214.70  
  Purchase #3 $9.59   10.667%   $10.613   $10.61   $10.60   $10.60  
  Purchase #4 $32.57   5.209%   $34.2666   $34.27   $34.25   $34.30  
  Purchase #5 $176.81   5.524%   $186.577   $186.58   $186.60   $186.60  
  Purchase #6 $180.68   12.826%   $203.854   $203.85   $203.85   $203.90  
  Purchase #7 $154.57   9.694%   $169.554   $169.55   $169.55   $169.60  
  7 purchase totals = $829.63       $896.0774   $896.07   $896.05   $896.20