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	$17.66	6.858%	$18.8711	$18.87	$18.85	$18.90
Purchase #2	$117.51	5.208%	$123.6299	$123.63	$123.65	$123.60
Purchase #3	$11.51	6.654%	$12.2759	$12.28	$12.30	$12.30
Purchase #4	$172.68	13.170%	$195.422	$195.42	$195.40	$195.40
Purchase #5	$174.72	4.108%	$181.8975	$181.90	$181.90	$181.90
Purchase #6	$110.45	11.457%	$123.1043	$123.10	$123.10	$123.10
Purchase #7	$50.30	10.158%	$55.4095	$55.41	$55.40	$55.40
7 purchase totals =	$654.83		$710.6102	$710.61	$710.60	$710.60