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	$127.74	8.105%	$138.0933	$138.09	$138.10	$138.10
Purchase #2	$163.74	3.442%	$169.3759	$169.38	$169.40	$169.40
Purchase #3	$165.39	4.179%	$172.3016	$172.30	$172.30	$172.30
Purchase #4	$119.92	3.105%	$123.6435	$123.64	$123.65	$123.60
Purchase #5	$80.30	3.733%	$83.2976	$83.30	$83.30	$83.30
Purchase #6	$33.51	3.236%	$34.5944	$34.59	$34.60	$34.60
Purchase #7	$130.31	12.367%	$146.4254	$146.43	$146.45	$146.40
7 purchase totals =	$820.91		$867.7317	$867.73	$867.80	$867.70