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 $31.57   8.788%   $34.3444   $34.34   $34.35   $34.30  
  Purchase #2 $54.99   12.787%   $62.0216   $62.02   $62.00   $62.00  
  Purchase #3 $185.82   5.461%   $195.9676   $195.97   $195.95   $196.00  
  Purchase #4 $131.68   3.382%   $136.1334   $136.13   $136.15   $136.10  
  Purchase #5 $208.91   3.797%   $216.8423   $216.84   $216.85   $216.80  
  Purchase #6 $237.62   4.601%   $248.5529   $248.55   $248.55   $248.60  
  Purchase #7 $84.69   11.316%   $94.2735   $94.27   $94.25   $94.30  
  7 purchase totals = $935.28       $988.1357   $988.12   $988.10   $988.10