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	$128.33	13.268%	$145.3568	$145.36	$145.35	$145.40
Purchase #2	$146.75	7.842%	$158.2581	$158.26	$158.25	$158.30
Purchase #3	$48.73	12.698%	$54.9177	$54.92	$54.90	$54.90
Purchase #4	$113.52	13.568%	$128.9224	$128.92	$128.90	$128.90
Purchase #5	$62.30	10.862%	$69.067	$69.07	$69.05	$69.10
Purchase #6	$47.70	6.725%	$50.9078	$50.91	$50.90	$50.90
Purchase #7	$28.29	13.432%	$32.0899	$32.09	$32.10	$32.10
7 purchase totals =	$575.62		$639.5197	$639.53	$639.45	$639.60