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	$121.29	11.123%	$134.7811	$134.78	$134.80	$134.80
Purchase #2	$200.87	8.337%	$217.6165	$217.62	$217.60	$217.60
Purchase #3	$30.80	7.152%	$33.0028	$33.00	$33.00	$33.00
Purchase #4	$74.61	4.621%	$78.0577	$78.06	$78.05	$78.10
Purchase #5	$130.83	11.123%	$145.3822	$145.38	$145.40	$145.40
Purchase #6	$49.31	10.175%	$54.3273	$54.33	$54.35	$54.30
Purchase #7	$230.27	3.543%	$238.4285	$238.43	$238.45	$238.40
7 purchase totals =	$837.98		$901.5961	$901.60	$901.65	$901.60