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	$21.57	13.569%	$24.4968	$24.50	$24.50	$24.50
Purchase #2	$41.41	5.279%	$43.596	$43.60	$43.60	$43.60
Purchase #3	$41.54	10.563%	$45.9279	$45.93	$45.95	$45.90
Purchase #4	$153.68	3.720%	$159.3969	$159.40	$159.40	$159.40
Purchase #5	$111.29	12.242%	$124.9141	$124.91	$124.90	$124.90
Purchase #6	$58.89	9.456%	$64.4586	$64.46	$64.45	$64.50
Purchase #7	$244.52	5.772%	$258.6337	$258.63	$258.65	$258.60
7 purchase totals =	$672.90		$721.4240	$721.43	$721.45	$721.40