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	$47.71	10.205%	$52.5788	$52.58	$52.60	$52.60
Purchase #2	$151.25	13.570%	$171.7746	$171.77	$171.75	$171.80
Purchase #3	$83.32	8.123%	$90.0881	$90.09	$90.10	$90.10
Purchase #4	$114.26	13.406%	$129.5777	$129.58	$129.60	$129.60
Purchase #5	$77.82	13.624%	$88.4222	$88.42	$88.40	$88.40
Purchase #6	$124.30	10.689%	$137.5864	$137.59	$137.60	$137.60
Purchase #7	$143.77	12.222%	$161.3416	$161.34	$161.35	$161.30
7 purchase totals =	$742.43		$831.3694	$831.37	$831.40	$831.40