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	$129.94	12.661%	$146.3917	$146.39	$146.40	$146.40
Purchase #2	$92.40	12.713%	$104.1468	$104.15	$104.15	$104.10
Purchase #3	$174.42	9.842%	$191.5864	$191.59	$191.60	$191.60
Purchase #4	$132.63	11.321%	$147.645	$147.65	$147.65	$147.60
Purchase #5	$106.62	4.554%	$111.4755	$111.48	$111.50	$111.50
Purchase #6	$240.97	10.479%	$266.2212	$266.22	$266.20	$266.20
Purchase #7	$141.91	11.525%	$158.2651	$158.27	$158.25	$158.30
7 purchase totals =	$1,018.89		$1,125.7317	$1,125.75	$1,125.75	$1,125.70