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	$248.79	10.683%	$275.3682	$275.37	$275.35	$275.40
Purchase #2	$179.45	3.397%	$185.5459	$185.55	$185.55	$185.50
Purchase #3	$144.94	6.293%	$154.0611	$154.06	$154.05	$154.10
Purchase #4	$139.87	9.111%	$152.6136	$152.61	$152.60	$152.60
Purchase #5	$34.52	13.268%	$39.1001	$39.10	$39.10	$39.10
Purchase #6	$33.26	5.652%	$35.1399	$35.14	$35.15	$35.10
Purchase #7	$153.71	4.246%	$160.2365	$160.24	$160.25	$160.20
7 purchase totals =	$934.54		$1,002.0653	$1,002.07	$1,002.05	$1,002.00