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 $167.49   9.243%   $182.9711   $182.97   $182.95   $183.00  
  Purchase #2 $32.48   8.758%   $35.3246   $35.32   $35.30   $35.30  
  Purchase #3 $133.45   5.613%   $140.9405   $140.94   $140.95   $140.90  
  Purchase #4 $250.86   8.184%   $271.3904   $271.39   $271.40   $271.40  
  Purchase #5 $117.72   8.137%   $127.2989   $127.30   $127.30   $127.30  
  Purchase #6 $228.38   3.654%   $236.725   $236.73   $236.75   $236.70  
  Purchase #7 $33.82   9.119%   $36.904   $36.90   $36.90   $36.90  
  7 purchase totals = $964.20       $1,031.5545   $1,031.55   $1,031.55   $1,031.50