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	$144.51	12.195%	$162.133	$162.13	$162.15	$162.10
Purchase #2	$138.51	3.836%	$143.8232	$143.82	$143.80	$143.80
Purchase #3	$192.52	4.146%	$200.5019	$200.50	$200.50	$200.50
Purchase #4	$20.69	8.698%	$22.4896	$22.49	$22.50	$22.50
Purchase #5	$48.63	13.754%	$55.3186	$55.32	$55.30	$55.30
Purchase #6	$160.89	10.731%	$178.1551	$178.16	$178.15	$178.20
Purchase #7	$204.30	9.723%	$224.1641	$224.16	$224.15	$224.20
7 purchase totals =	$910.05		$986.5855	$986.58	$986.55	$986.60