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	$27.93	8.381%	$30.2708	$30.27	$30.25	$30.30
Purchase #2	$127.95	10.683%	$141.6189	$141.62	$141.60	$141.60
Purchase #3	$173.25	13.364%	$196.4031	$196.40	$196.40	$196.40
Purchase #4	$93.73	5.394%	$98.7858	$98.79	$98.80	$98.80
Purchase #5	$215.85	3.168%	$222.6881	$222.69	$222.70	$222.70
Purchase #6	$220.25	12.251%	$247.2328	$247.23	$247.25	$247.20
Purchase #7	$103.51	4.488%	$108.1555	$108.16	$108.15	$108.20
7 purchase totals =	$962.47		$1,045.1550	$1,045.16	$1,045.15	$1,045.20