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	$15.88	4.290%	$16.5613	$16.56	$16.55	$16.60
Purchase #2	$5.87	11.730%	$6.5586	$6.56	$6.55	$6.60
Purchase #3	$38.78	4.303%	$40.4487	$40.45	$40.45	$40.40
Purchase #4	$20.72	5.615%	$21.8834	$21.88	$21.90	$21.90
Purchase #5	$108.59	3.837%	$112.7566	$112.76	$112.75	$112.80
Purchase #6	$50.63	7.268%	$54.3098	$54.31	$54.30	$54.30
Purchase #7	$134.65	9.842%	$147.9023	$147.90	$147.90	$147.90
7 purchase totals =	$375.12		$400.4207	$400.42	$400.40	$400.50