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	$235.85	11.649%	$263.3242	$263.32	$263.30	$263.30
Purchase #2	$145.47	3.222%	$150.157	$150.16	$150.15	$150.20
Purchase #3	$140.82	13.495%	$159.8237	$159.82	$159.80	$159.80
Purchase #4	$20.52	8.835%	$22.3329	$22.33	$22.35	$22.30
Purchase #5	$244.27	4.408%	$255.0374	$255.04	$255.05	$255.00
Purchase #6	$230.25	13.412%	$261.1311	$261.13	$261.15	$261.10
Purchase #7	$34.28	8.170%	$37.0807	$37.08	$37.10	$37.10
7 purchase totals =	$1,051.46		$1,148.8870	$1,148.88	$1,148.90	$1,148.80