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	$6.91	10.301%	$7.6218	$7.62	$7.60	$7.60
Purchase #2	$145.89	6.754%	$155.7434	$155.74	$155.75	$155.70
Purchase #3	$34.86	7.757%	$37.5641	$37.56	$37.55	$37.60
Purchase #4	$204.88	4.664%	$214.4356	$214.44	$214.45	$214.40
Purchase #5	$166.69	3.535%	$172.5825	$172.58	$172.60	$172.60
Purchase #6	$94.82	5.565%	$100.0967	$100.10	$100.10	$100.10
Purchase #7	$109.94	10.156%	$121.1055	$121.11	$121.10	$121.10
7 purchase totals =	$763.99		$809.1496	$809.15	$809.15	$809.10