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	$5.38	13.244%	$6.0925	$6.09	$6.10	$6.10
Purchase #2	$100.92	4.310%	$105.2697	$105.27	$105.25	$105.30
Purchase #3	$15.32	11.142%	$17.027	$17.03	$17.05	$17.00
Purchase #4	$115.62	10.448%	$127.7	$127.70	$127.70	$127.70
Purchase #5	$175.77	6.731%	$187.6011	$187.60	$187.60	$187.60
Purchase #6	$116.73	10.162%	$128.5921	$128.59	$128.60	$128.60
Purchase #7	$54.82	9.449%	$59.9999	$60.00	$60.00	$60.00
7 purchase totals =	$584.56		$632.2823	$632.28	$632.30	$632.30