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	$100.93	10.385%	$111.4116	$111.41	$111.40	$111.40
Purchase #2	$13.75	12.740%	$15.5018	$15.50	$15.50	$15.50
Purchase #3	$172.29	8.657%	$187.2051	$187.21	$187.20	$187.20
Purchase #4	$101.47	7.730%	$109.3136	$109.31	$109.30	$109.30
Purchase #5	$46.64	13.832%	$53.0912	$53.09	$53.10	$53.10
Purchase #6	$56.58	7.495%	$60.8207	$60.82	$60.80	$60.80
Purchase #7	$165.52	7.167%	$177.3828	$177.38	$177.40	$177.40
7 purchase totals =	$657.18		$714.7268	$714.72	$714.70	$714.70