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	$240.96	10.634%	$266.5837	$266.58	$266.60	$266.60
Purchase #2	$146.41	11.241%	$162.8679	$162.87	$162.85	$162.90
Purchase #3	$176.29	9.799%	$193.5647	$193.56	$193.55	$193.60
Purchase #4	$55.59	3.311%	$57.4306	$57.43	$57.45	$57.40
Purchase #5	$129.51	11.189%	$144.0009	$144.00	$144.00	$144.00
Purchase #6	$138.35	12.198%	$155.2259	$155.23	$155.25	$155.20
Purchase #7	$93.67	13.659%	$106.4644	$106.46	$106.45	$106.50
7 purchase totals =	$980.78		$1,086.1381	$1,086.13	$1,086.15	$1,086.20