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	$57.29	6.471%	$60.9972	$61.00	$61.00	$61.00
Purchase #2	$189.30	8.762%	$205.8865	$205.89	$205.90	$205.90
Purchase #3	$11.54	12.238%	$12.9523	$12.95	$12.95	$13.00
Purchase #4	$148.69	3.844%	$154.4056	$154.41	$154.40	$154.40
Purchase #5	$236.27	8.681%	$256.7806	$256.78	$256.80	$256.80
Purchase #6	$236.49	8.619%	$256.8731	$256.87	$256.85	$256.90
Purchase #7	$120.92	9.596%	$132.5235	$132.52	$132.50	$132.50
7 purchase totals =	$1,000.50		$1,080.4188	$1,080.42	$1,080.40	$1,080.50