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	$57.62	6.429%	$61.3244	$61.32	$61.30	$61.30
Purchase #2	$139.71	4.611%	$146.152	$146.15	$146.15	$146.20
Purchase #3	$158.51	7.615%	$170.5805	$170.58	$170.60	$170.60
Purchase #4	$216.94	3.406%	$224.329	$224.33	$224.35	$224.30
Purchase #5	$42.30	9.504%	$46.3202	$46.32	$46.30	$46.30
Purchase #6	$205.56	11.259%	$228.704	$228.70	$228.70	$228.70
Purchase #7	$78.33	5.659%	$82.7627	$82.76	$82.75	$82.80
7 purchase totals =	$898.97		$960.1728	$960.16	$960.15	$960.20