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	$17.92	3.442%	$18.5368	$18.54	$18.55	$18.50
Purchase #2	$146.82	8.860%	$159.8283	$159.83	$159.85	$159.80
Purchase #3	$164.49	6.162%	$174.6259	$174.63	$174.65	$174.60
Purchase #4	$241.56	6.244%	$256.643	$256.64	$256.65	$256.60
Purchase #5	$242.51	13.135%	$274.3637	$274.36	$274.35	$274.40
Purchase #6	$70.79	11.388%	$78.8516	$78.85	$78.85	$78.90
Purchase #7	$58.28	12.532%	$65.5836	$65.58	$65.60	$65.60
7 purchase totals =	$942.37		$1,028.4329	$1,028.43	$1,028.50	$1,028.40