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	$105.98	5.422%	$111.7262	$111.73	$111.75	$111.70
Purchase #2	$34.73	8.687%	$37.747	$37.75	$37.75	$37.70
Purchase #3	$50.72	9.588%	$55.583	$55.58	$55.60	$55.60
Purchase #4	$191.49	13.445%	$217.2358	$217.24	$217.25	$217.20
Purchase #5	$40.77	10.852%	$45.1944	$45.19	$45.20	$45.20
Purchase #6	$42.83	9.284%	$46.8063	$46.81	$46.80	$46.80
Purchase #7	$136.58	10.700%	$151.1941	$151.19	$151.20	$151.20
7 purchase totals =	$603.10		$665.4868	$665.49	$665.55	$665.40