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	$34.68	10.768%	$38.4143	$38.41	$38.40	$38.40
Purchase #2	$122.71	3.612%	$127.1423	$127.14	$127.15	$127.10
Purchase #3	$63.60	4.770%	$66.6337	$66.63	$66.65	$66.60
Purchase #4	$149.78	9.645%	$164.2263	$164.23	$164.25	$164.20
Purchase #5	$237.99	5.186%	$250.3322	$250.33	$250.35	$250.30
Purchase #6	$92.62	7.762%	$99.8092	$99.81	$99.80	$99.80
Purchase #7	$17.90	11.563%	$19.9698	$19.97	$19.95	$20.00
7 purchase totals =	$719.28		$766.5278	$766.52	$766.55	$766.40