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	$159.27	9.773%	$174.8355	$174.84	$174.85	$174.80
Purchase #2	$101.74	9.544%	$111.4501	$111.45	$111.45	$111.50
Purchase #3	$59.78	9.457%	$65.4334	$65.43	$65.45	$65.40
Purchase #4	$56.46	4.808%	$59.1746	$59.17	$59.15	$59.20
Purchase #5	$12.41	11.299%	$13.8122	$13.81	$13.80	$13.80
Purchase #6	$177.65	5.599%	$187.5966	$187.60	$187.60	$187.60
Purchase #7	$26.58	12.117%	$29.8007	$29.80	$29.80	$29.80
7 purchase totals =	$593.89		$642.1031	$642.10	$642.10	$642.10