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	$239.92	10.584%	$265.3131	$265.31	$265.30	$265.30
Purchase #2	$127.83	13.139%	$144.6256	$144.63	$144.65	$144.60
Purchase #3	$50.95	13.502%	$57.8293	$57.83	$57.85	$57.80
Purchase #4	$146.40	4.664%	$153.2281	$153.23	$153.25	$153.20
Purchase #5	$146.76	5.743%	$155.1884	$155.19	$155.20	$155.20
Purchase #6	$151.84	13.665%	$172.5889	$172.59	$172.60	$172.60
Purchase #7	$81.60	11.707%	$91.1529	$91.15	$91.15	$91.20
7 purchase totals =	$945.30		$1,039.9263	$1,039.93	$1,040.00	$1,039.90