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	$37.49	6.723%	$40.0105	$40.01	$40.00	$40.00
Purchase #2	$48.88	5.244%	$51.4433	$51.44	$51.45	$51.40
Purchase #3	$10.54	12.565%	$11.8644	$11.86	$11.85	$11.90
Purchase #4	$181.97	10.105%	$200.3581	$200.36	$200.35	$200.40
Purchase #5	$101.50	10.269%	$111.923	$111.92	$111.90	$111.90
Purchase #6	$129.87	10.479%	$143.4791	$143.48	$143.50	$143.50
Purchase #7	$14.55	10.563%	$16.0869	$16.09	$16.10	$16.10
7 purchase totals =	$524.80		$575.1653	$575.16	$575.15	$575.20