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	$245.80	13.335%	$278.5774	$278.58	$278.60	$278.60
Purchase #2	$99.66	7.376%	$107.0109	$107.01	$107.00	$107.00
Purchase #3	$143.46	10.287%	$158.2177	$158.22	$158.20	$158.20
Purchase #4	$96.83	9.264%	$105.8003	$105.80	$105.80	$105.80
Purchase #5	$146.32	5.288%	$154.0574	$154.06	$154.05	$154.10
Purchase #6	$94.59	11.439%	$105.4102	$105.41	$105.40	$105.40
Purchase #7	$207.26	3.309%	$214.1182	$214.12	$214.10	$214.10
7 purchase totals =	$1,033.92		$1,123.1921	$1,123.20	$1,123.15	$1,123.20