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	$244.94	4.636%	$256.2954	$256.30	$256.30	$256.30
Purchase #2	$18.40	8.827%	$20.0242	$20.02	$20.00	$20.00
Purchase #3	$60.86	6.177%	$64.6193	$64.62	$64.60	$64.60
Purchase #4	$233.51	6.343%	$248.3215	$248.32	$248.30	$248.30
Purchase #5	$194.84	11.596%	$217.4336	$217.43	$217.45	$217.40
Purchase #6	$88.37	12.839%	$99.7158	$99.72	$99.70	$99.70
Purchase #7	$226.44	6.697%	$241.6047	$241.60	$241.60	$241.60
7 purchase totals =	$1,067.36		$1,148.0145	$1,148.01	$1,147.95	$1,147.90