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	$74.53	8.122%	$80.5833	$80.58	$80.60	$80.60
Purchase #2	$229.71	11.542%	$256.2231	$256.22	$256.20	$256.20
Purchase #3	$117.58	9.262%	$128.4703	$128.47	$128.45	$128.50
Purchase #4	$129.67	5.479%	$136.7746	$136.77	$136.75	$136.80
Purchase #5	$96.55	4.580%	$100.972	$100.97	$100.95	$101.00
Purchase #6	$180.50	6.160%	$191.6188	$191.62	$191.60	$191.60
Purchase #7	$37.89	3.699%	$39.2916	$39.29	$39.30	$39.30
7 purchase totals =	$866.43		$933.9337	$933.92	$933.85	$934.00