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	$37.28	4.426%	$38.93	$38.93	$38.95	$38.90
Purchase #2	$121.60	4.714%	$127.3322	$127.33	$127.35	$127.30
Purchase #3	$208.25	5.718%	$220.1577	$220.16	$220.15	$220.20
Purchase #4	$237.75	11.658%	$265.4669	$265.47	$265.45	$265.50
Purchase #5	$49.59	3.109%	$51.1318	$51.13	$51.15	$51.10
Purchase #6	$113.42	13.325%	$128.5332	$128.53	$128.55	$128.50
Purchase #7	$147.80	7.205%	$158.449	$158.45	$158.45	$158.40
7 purchase totals =	$915.69		$990.0008	$990.00	$990.05	$989.90