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	$232.92	13.564%	$264.5133	$264.51	$264.50	$264.50
Purchase #2	$126.67	12.189%	$142.1098	$142.11	$142.10	$142.10
Purchase #3	$222.92	3.354%	$230.3967	$230.40	$230.40	$230.40
Purchase #4	$87.40	3.150%	$90.1531	$90.15	$90.15	$90.20
Purchase #5	$200.54	4.554%	$209.6726	$209.67	$209.65	$209.70
Purchase #6	$214.60	11.565%	$239.4185	$239.42	$239.40	$239.40
Purchase #7	$148.53	12.107%	$166.5125	$166.51	$166.50	$166.50
7 purchase totals =	$1,233.58		$1,342.7765	$1,342.77	$1,342.70	$1,342.80