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	$80.97	10.683%	$89.62	$89.62	$89.60	$89.60
Purchase #2	$59.57	9.397%	$65.1678	$65.17	$65.15	$65.20
Purchase #3	$12.92	9.506%	$14.1482	$14.15	$14.15	$14.10
Purchase #4	$144.88	5.757%	$153.2207	$153.22	$153.20	$153.20
Purchase #5	$111.95	4.435%	$116.915	$116.92	$116.90	$116.90
Purchase #6	$154.40	9.792%	$169.5188	$169.52	$169.50	$169.50
Purchase #7	$158.25	5.450%	$166.8746	$166.87	$166.85	$166.90
7 purchase totals =	$722.94		$775.4651	$775.47	$775.35	$775.40