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	$10.87	7.861%	$11.7245	$11.72	$11.70	$11.70
Purchase #2	$176.44	12.335%	$198.2039	$198.20	$198.20	$198.20
Purchase #3	$103.97	7.535%	$111.8041	$111.80	$111.80	$111.80
Purchase #4	$43.69	4.491%	$45.6521	$45.65	$45.65	$45.70
Purchase #5	$68.62	3.627%	$71.1088	$71.11	$71.10	$71.10
Purchase #6	$149.50	11.344%	$166.4593	$166.46	$166.45	$166.50
Purchase #7	$235.60	5.486%	$248.525	$248.53	$248.55	$248.50
7 purchase totals =	$788.69		$853.4777	$853.47	$853.45	$853.50