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	$30.28	7.299%	$32.4901	$32.49	$32.50	$32.50
Purchase #2	$127.37	10.772%	$141.0903	$141.09	$141.10	$141.10
Purchase #3	$231.41	10.697%	$256.1639	$256.16	$256.15	$256.20
Purchase #4	$170.50	3.667%	$176.7522	$176.75	$176.75	$176.80
Purchase #5	$208.37	6.485%	$221.8828	$221.88	$221.90	$221.90
Purchase #6	$104.92	12.540%	$118.077	$118.08	$118.10	$118.10
Purchase #7	$126.43	4.274%	$131.8336	$131.83	$131.85	$131.80
7 purchase totals =	$999.28		$1,078.2899	$1,078.28	$1,078.35	$1,078.40