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	$93.82	10.845%	$103.9948	$103.99	$104.00	$104.00
Purchase #2	$180.68	13.766%	$205.5524	$205.55	$205.55	$205.60
Purchase #3	$115.54	13.514%	$131.1541	$131.15	$131.15	$131.20
Purchase #4	$110.59	7.281%	$118.6421	$118.64	$118.65	$118.60
Purchase #5	$125.26	13.739%	$142.4695	$142.47	$142.45	$142.50
Purchase #6	$90.59	13.846%	$103.1331	$103.13	$103.15	$103.10
Purchase #7	$144.82	4.720%	$151.6555	$151.66	$151.65	$151.70
7 purchase totals =	$861.30		$956.6015	$956.59	$956.60	$956.70