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	$80.49	9.236%	$87.9241	$87.92	$87.90	$87.90
Purchase #2	$166.70	3.447%	$172.4461	$172.45	$172.45	$172.40
Purchase #3	$145.27	4.624%	$151.9873	$151.99	$152.00	$152.00
Purchase #4	$77.82	7.237%	$83.4518	$83.45	$83.45	$83.50
Purchase #5	$87.30	13.728%	$99.2845	$99.28	$99.30	$99.30
Purchase #6	$47.41	7.230%	$50.8377	$50.84	$50.85	$50.80
Purchase #7	$241.57	6.105%	$256.3178	$256.32	$256.30	$256.30
7 purchase totals =	$846.56		$902.2493	$902.25	$902.25	$902.20