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	$236.77	8.239%	$256.2775	$256.28	$256.30	$256.30
Purchase #2	$18.26	7.195%	$19.5738	$19.57	$19.55	$19.60
Purchase #3	$226.41	12.749%	$255.275	$255.28	$255.30	$255.30
Purchase #4	$90.72	3.654%	$94.0349	$94.03	$94.05	$94.00
Purchase #5	$99.48	3.388%	$102.8504	$102.85	$102.85	$102.90
Purchase #6	$82.33	12.607%	$92.7093	$92.71	$92.70	$92.70
Purchase #7	$62.38	5.539%	$65.8352	$65.84	$65.85	$65.80
7 purchase totals =	$816.35		$886.5561	$886.56	$886.60	$886.60