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 $164.44   11.122%   $182.729   $182.73   $182.75   $182.70  
  Purchase #2 $249.88   9.709%   $274.1408   $274.14   $274.15   $274.10  
  Purchase #3 $210.81   8.141%   $227.972   $227.97   $227.95   $228.00  
  Purchase #4 $240.50   3.145%   $248.0637   $248.06   $248.05   $248.10  
  Purchase #5 $89.60   7.807%   $96.5951   $96.60   $96.60   $96.60  
  Purchase #6 $190.91   13.859%   $217.3682   $217.37   $217.35   $217.40  
  Purchase #7 $177.77   13.758%   $202.2276   $202.23   $202.25   $202.20  
  7 purchase totals = $1,323.91       $1,449.0964   $1,449.10   $1,449.10   $1,449.10