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 $192.25   3.337%   $198.6654   $198.67   $198.65   $198.70  
  Purchase #2 $250.89   9.509%   $274.7471   $274.75   $274.75   $274.70  
  Purchase #3 $41.57   3.672%   $43.0965   $43.10   $43.10   $43.10  
  Purchase #4 $183.64   6.699%   $195.942   $195.94   $195.95   $195.90  
  Purchase #5 $70.40   8.479%   $76.3692   $76.37   $76.35   $76.40  
  Purchase #6 $164.90   10.608%   $182.3926   $182.39   $182.40   $182.40  
  Purchase #7 $87.99   9.498%   $96.3473   $96.35   $96.35   $96.30  
  7 purchase totals = $991.64       $1,067.5601   $1,067.57   $1,067.55   $1,067.50