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	$241.83	5.136%	$254.2504	$254.25	$254.25	$254.30
Purchase #2	$25.91	5.106%	$27.233	$27.23	$27.25	$27.20
Purchase #3	$217.82	8.723%	$236.8204	$236.82	$236.80	$236.80
Purchase #4	$81.92	4.263%	$85.4122	$85.41	$85.40	$85.40
Purchase #5	$201.29	10.111%	$221.6424	$221.64	$221.65	$221.60
Purchase #6	$111.45	10.692%	$123.3662	$123.37	$123.35	$123.40
Purchase #7	$9.67	11.552%	$10.7871	$10.79	$10.80	$10.80
7 purchase totals =	$889.89		$959.5117	$959.51	$959.50	$959.50