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 $202.82   9.635%   $222.3617   $222.36   $222.35   $222.40  
  Purchase #2 $41.27   7.822%   $44.4981   $44.50   $44.50   $44.50  
  Purchase #3 $222.65   8.335%   $241.2079   $241.21   $241.20   $241.20  
  Purchase #4 $123.37   9.388%   $134.952   $134.95   $134.95   $135.00  
  Purchase #5 $130.73   5.103%   $137.4012   $137.40   $137.40   $137.40  
  Purchase #6 $175.46   6.225%   $186.3824   $186.38   $186.40   $186.40  
  Purchase #7 $72.96   6.865%   $77.9687   $77.97   $77.95   $78.00  
  7 purchase totals = $969.26       $1,044.7720   $1,044.77   $1,044.75   $1,044.90