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	$76.35	8.421%	$82.7794	$82.78	$82.80	$82.80
Purchase #2	$230.70	9.331%	$252.2266	$252.23	$252.25	$252.20
Purchase #3	$89.81	10.833%	$99.5391	$99.54	$99.55	$99.50
Purchase #4	$42.39	13.559%	$48.1377	$48.14	$48.15	$48.10
Purchase #5	$41.76	5.184%	$43.9248	$43.92	$43.90	$43.90
Purchase #6	$22.93	4.379%	$23.9341	$23.93	$23.95	$23.90
Purchase #7	$150.48	11.539%	$167.8439	$167.84	$167.85	$167.80
7 purchase totals =	$654.42		$718.3856	$718.38	$718.45	$718.20