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	$125.66	4.306%	$131.0709	$131.07	$131.05	$131.10
Purchase #2	$65.37	13.521%	$74.2087	$74.21	$74.20	$74.20
Purchase #3	$248.87	9.624%	$272.8212	$272.82	$272.80	$272.80
Purchase #4	$114.88	7.170%	$123.1169	$123.12	$123.10	$123.10
Purchase #5	$172.28	4.742%	$180.4495	$180.45	$180.45	$180.40
Purchase #6	$105.60	5.280%	$111.1757	$111.18	$111.20	$111.20
Purchase #7	$5.95	11.622%	$6.6415	$6.64	$6.65	$6.60
7 purchase totals =	$838.61		$899.4844	$899.49	$899.45	$899.40