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	$144.72	11.194%	$160.92	$160.92	$160.90	$160.90
Purchase #2	$30.83	13.205%	$34.9011	$34.90	$34.90	$34.90
Purchase #3	$143.78	10.304%	$158.5951	$158.60	$158.60	$158.60
Purchase #4	$57.60	6.422%	$61.2991	$61.30	$61.30	$61.30
Purchase #5	$195.33	12.631%	$220.0021	$220.00	$220.00	$220.00
Purchase #6	$182.97	8.353%	$198.2535	$198.25	$198.25	$198.30
Purchase #7	$54.84	12.365%	$61.621	$61.62	$61.60	$61.60
7 purchase totals =	$810.07		$895.5919	$895.59	$895.55	$895.60