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 $48.77   8.609%   $52.9686   $52.97   $52.95   $53.00  
  Purchase #2 $186.87   8.755%   $203.2305   $203.23   $203.25   $203.20  
  Purchase #3 $244.53   3.461%   $252.9932   $252.99   $253.00   $253.00  
  Purchase #4 $92.61   3.226%   $95.5976   $95.60   $95.60   $95.60  
  Purchase #5 $26.97   11.339%   $30.0281   $30.03   $30.05   $30.00  
  Purchase #6 $239.51   3.715%   $248.4078   $248.41   $248.40   $248.40  
  Purchase #7 $151.45   6.407%   $161.1534   $161.15   $161.15   $161.20  
  7 purchase totals = $990.71       $1,044.3792   $1,044.38   $1,044.40   $1,044.40