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 $217.58   5.146%   $228.7767   $228.78   $228.80   $228.80  
  Purchase #2 $151.38   10.479%   $167.2431   $167.24   $167.25   $167.20  
  Purchase #3 $231.99   7.296%   $248.916   $248.92   $248.90   $248.90  
  Purchase #4 $119.49   6.861%   $127.6882   $127.69   $127.70   $127.70  
  Purchase #5 $236.90   12.141%   $265.662   $265.66   $265.65   $265.70  
  Purchase #6 $237.53   10.244%   $261.8626   $261.86   $261.85   $261.90  
  Purchase #7 $77.48   8.612%   $84.1526   $84.15   $84.15   $84.20  
  7 purchase totals = $1,272.35       $1,384.3012   $1,384.30   $1,384.30   $1,384.40