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 $196.75   5.738%   $208.0395   $208.04   $208.05   $208.00  
  Purchase #2 $202.36   7.622%   $217.7839   $217.78   $217.80   $217.80  
  Purchase #3 $240.50   3.692%   $249.3793   $249.38   $249.40   $249.40  
  Purchase #4 $180.55   6.497%   $192.2803   $192.28   $192.30   $192.30  
  Purchase #5 $183.92   8.129%   $198.8709   $198.87   $198.85   $198.90  
  Purchase #6 $102.40   4.546%   $107.0551   $107.06   $107.05   $107.10  
  Purchase #7 $58.71   9.354%   $64.2017   $64.20   $64.20   $64.20  
  7 purchase totals = $1,165.19       $1,237.6107   $1,237.61   $1,237.65   $1,237.70