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	$16.91	9.537%	$18.5227	$18.52	$18.50	$18.50
Purchase #2	$103.36	7.632%	$111.2484	$111.25	$111.25	$111.20
Purchase #3	$145.43	5.728%	$153.7602	$153.76	$153.75	$153.80
Purchase #4	$119.99	4.109%	$124.9204	$124.92	$124.90	$124.90
Purchase #5	$74.85	7.426%	$80.4084	$80.41	$80.40	$80.40
Purchase #6	$166.49	12.866%	$187.9106	$187.91	$187.90	$187.90
Purchase #7	$237.53	12.244%	$266.6132	$266.61	$266.60	$266.60
7 purchase totals =	$864.56		$943.3839	$943.38	$943.30	$943.30