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	$85.61	4.414%	$89.3888	$89.39	$89.40	$89.40
Purchase #2	$48.78	5.739%	$51.5795	$51.58	$51.60	$51.60
Purchase #3	$9.68	11.760%	$10.8184	$10.82	$10.80	$10.80
Purchase #4	$27.50	4.334%	$28.6919	$28.69	$28.70	$28.70
Purchase #5	$214.37	6.509%	$228.3233	$228.32	$228.30	$228.30
Purchase #6	$29.61	8.461%	$32.1153	$32.12	$32.10	$32.10
Purchase #7	$82.39	11.554%	$91.9093	$91.91	$91.90	$91.90
7 purchase totals =	$497.94		$532.8265	$532.83	$532.80	$532.80