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	$77.89	12.575%	$87.6847	$87.68	$87.70	$87.70
Purchase #2	$226.43	3.468%	$234.2826	$234.28	$234.30	$234.30
Purchase #3	$159.88	4.589%	$167.2169	$167.22	$167.20	$167.20
Purchase #4	$93.39	10.434%	$103.1343	$103.13	$103.15	$103.10
Purchase #5	$19.50	5.403%	$20.5536	$20.55	$20.55	$20.60
Purchase #6	$80.75	12.478%	$90.826	$90.83	$90.85	$90.80
Purchase #7	$183.94	13.688%	$209.1177	$209.12	$209.10	$209.10
7 purchase totals =	$841.78		$912.8158	$912.81	$912.85	$912.80