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 $85.94   10.608%   $95.0565   $95.06   $95.05   $95.10  
  Purchase #2 $32.56   11.737%   $36.3816   $36.38   $36.40   $36.40  
  Purchase #3 $242.36   9.548%   $265.5005   $265.50   $265.50   $265.50  
  Purchase #4 $76.58   8.255%   $82.9017   $82.90   $82.90   $82.90  
  Purchase #5 $91.93   13.771%   $104.5897   $104.59   $104.60   $104.60  
  Purchase #6 $223.88   4.729%   $234.4673   $234.47   $234.45   $234.50  
  Purchase #7 $91.58   7.214%   $98.1866   $98.19   $98.20   $98.20  
  7 purchase totals = $844.83       $917.0839   $917.09   $917.10   $917.20