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	$146.86	6.486%	$156.3853	$156.39	$156.40	$156.40
Purchase #2	$71.32	8.186%	$77.1583	$77.16	$77.15	$77.20
Purchase #3	$11.53	8.536%	$12.5142	$12.51	$12.50	$12.50
Purchase #4	$40.28	12.130%	$45.166	$45.17	$45.15	$45.20
Purchase #5	$155.36	10.870%	$172.2476	$172.25	$172.25	$172.20
Purchase #6	$201.30	5.683%	$212.7399	$212.74	$212.75	$212.70
Purchase #7	$107.60	11.584%	$120.0644	$120.06	$120.05	$120.10
7 purchase totals =	$734.25		$796.2757	$796.28	$796.25	$796.30