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	$90.76	9.541%	$99.4194	$99.42	$99.40	$99.40
Purchase #2	$137.79	4.387%	$143.8348	$143.83	$143.85	$143.80
Purchase #3	$235.56	7.185%	$252.485	$252.49	$252.50	$252.50
Purchase #4	$137.72	11.784%	$153.9489	$153.95	$153.95	$153.90
Purchase #5	$229.94	7.344%	$246.8268	$246.83	$246.85	$246.80
Purchase #6	$117.85	4.446%	$123.0896	$123.09	$123.10	$123.10
Purchase #7	$78.94	6.286%	$83.9022	$83.90	$83.90	$83.90
7 purchase totals =	$1,028.56		$1,103.5067	$1,103.51	$1,103.55	$1,103.40