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 $186.79   11.813%   $208.8555   $208.86   $208.85   $208.90  
  Purchase #2 $57.99   13.582%   $65.8662   $65.87   $65.85   $65.90  
  Purchase #3 $8.34   8.288%   $9.0312   $9.03   $9.05   $9.00  
  Purchase #4 $73.86   3.137%   $76.177   $76.18   $76.20   $76.20  
  Purchase #5 $183.43   3.587%   $190.0096   $190.01   $190.00   $190.00  
  Purchase #6 $242.68   13.445%   $275.3083   $275.31   $275.30   $275.30  
  Purchase #7 $199.38   4.299%   $207.9513   $207.95   $207.95   $208.00  
  7 purchase totals = $952.47       $1,033.1991   $1,033.21   $1,033.20   $1,033.30