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	$70.78	13.631%	$80.428	$80.43	$80.45	$80.40
Purchase #2	$110.70	11.397%	$123.3165	$123.32	$123.30	$123.30
Purchase #3	$45.72	4.572%	$47.8103	$47.81	$47.80	$47.80
Purchase #4	$36.51	4.784%	$38.2566	$38.26	$38.25	$38.30
Purchase #5	$35.98	8.119%	$38.9012	$38.90	$38.90	$38.90
Purchase #6	$101.31	10.251%	$111.6953	$111.70	$111.70	$111.70
Purchase #7	$112.77	12.301%	$126.6418	$126.64	$126.65	$126.60
7 purchase totals =	$513.77		$567.0497	$567.06	$567.05	$567.00