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	$37.66	5.133%	$39.5931	$39.59	$39.60	$39.60
Purchase #2	$46.54	7.798%	$50.1692	$50.17	$50.15	$50.20
Purchase #3	$139.78	3.184%	$144.2306	$144.23	$144.25	$144.20
Purchase #4	$70.94	11.437%	$79.0534	$79.05	$79.05	$79.10
Purchase #5	$241.45	7.307%	$259.0928	$259.09	$259.10	$259.10
Purchase #6	$68.98	10.854%	$76.4671	$76.47	$76.45	$76.50
Purchase #7	$101.60	9.400%	$111.1504	$111.15	$111.15	$111.20
7 purchase totals =	$706.95		$759.7566	$759.75	$759.75	$759.90