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	$115.40	10.852%	$127.9232	$127.92	$127.90	$127.90
Purchase #2	$86.84	13.375%	$98.4549	$98.45	$98.45	$98.50
Purchase #3	$86.66	10.300%	$95.586	$95.59	$95.60	$95.60
Purchase #4	$122.28	4.448%	$127.719	$127.72	$127.70	$127.70
Purchase #5	$37.39	8.825%	$40.6897	$40.69	$40.70	$40.70
Purchase #6	$23.93	7.436%	$25.7094	$25.71	$25.70	$25.70
Purchase #7	$13.27	5.379%	$13.9838	$13.98	$14.00	$14.00
7 purchase totals =	$485.77		$530.0660	$530.06	$530.05	$530.10