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	$81.42	10.634%	$90.0782	$90.08	$90.10	$90.10
Purchase #2	$112.34	6.664%	$119.8263	$119.83	$119.85	$119.80
Purchase #3	$5.66	9.404%	$6.1923	$6.19	$6.20	$6.20
Purchase #4	$11.46	8.261%	$12.4067	$12.41	$12.40	$12.40
Purchase #5	$233.54	13.233%	$264.4443	$264.44	$264.45	$264.40
Purchase #6	$207.34	6.222%	$220.2407	$220.24	$220.25	$220.20
Purchase #7	$154.63	11.513%	$172.4326	$172.43	$172.45	$172.40
7 purchase totals =	$806.39		$885.6211	$885.62	$885.70	$885.50