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	$159.51	11.580%	$177.9813	$177.98	$178.00	$178.00
Purchase #2	$86.72	3.847%	$90.0561	$90.06	$90.05	$90.10
Purchase #3	$204.81	12.430%	$230.2679	$230.27	$230.25	$230.30
Purchase #4	$64.37	11.772%	$71.9476	$71.95	$71.95	$71.90
Purchase #5	$65.76	9.717%	$72.1499	$72.15	$72.15	$72.10
Purchase #6	$21.78	12.260%	$24.4502	$24.45	$24.45	$24.50
Purchase #7	$108.94	6.773%	$116.3185	$116.32	$116.30	$116.30
7 purchase totals =	$711.89		$783.1715	$783.18	$783.15	$783.20