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	$72.82	12.116%	$81.6429	$81.64	$81.65	$81.60
Purchase #2	$49.79	12.316%	$55.9221	$55.92	$55.90	$55.90
Purchase #3	$200.69	9.860%	$220.478	$220.48	$220.50	$220.50
Purchase #4	$139.44	4.752%	$146.0662	$146.07	$146.05	$146.10
Purchase #5	$237.60	5.565%	$250.8224	$250.82	$250.80	$250.80
Purchase #6	$128.82	13.389%	$146.0677	$146.07	$146.05	$146.10
Purchase #7	$170.59	8.684%	$185.404	$185.40	$185.40	$185.40
7 purchase totals =	$999.75		$1,086.4033	$1,086.40	$1,086.35	$1,086.40