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	$171.71	4.163%	$178.8583	$178.86	$178.85	$178.90
Purchase #2	$126.28	8.860%	$137.4684	$137.47	$137.45	$137.50
Purchase #3	$199.27	5.613%	$210.455	$210.46	$210.45	$210.50
Purchase #4	$158.81	5.431%	$167.435	$167.44	$167.45	$167.40
Purchase #5	$92.55	8.598%	$100.5074	$100.51	$100.50	$100.50
Purchase #6	$76.52	12.121%	$85.795	$85.80	$85.80	$85.80
Purchase #7	$94.84	7.188%	$101.6571	$101.66	$101.65	$101.70
7 purchase totals =	$919.98		$982.1762	$982.20	$982.15	$982.30