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	$166.50	10.560%	$184.0824	$184.08	$184.10	$184.10
Purchase #2	$179.69	9.526%	$196.8073	$196.81	$196.80	$196.80
Purchase #3	$127.70	4.172%	$133.0276	$133.03	$133.05	$133.00
Purchase #4	$7.50	13.460%	$8.5095	$8.51	$8.50	$8.50
Purchase #5	$55.52	7.523%	$59.6968	$59.70	$59.70	$59.70
Purchase #6	$95.42	11.739%	$106.6214	$106.62	$106.60	$106.60
Purchase #7	$126.91	3.296%	$131.093	$131.09	$131.10	$131.10
7 purchase totals =	$759.24		$819.8380	$819.84	$819.85	$819.80