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	$8.41	7.133%	$9.0099	$9.01	$9.00	$9.00
Purchase #2	$101.37	9.627%	$111.1289	$111.13	$111.15	$111.10
Purchase #3	$143.93	5.391%	$151.6893	$151.69	$151.70	$151.70
Purchase #4	$10.72	10.697%	$11.8667	$11.87	$11.85	$11.90
Purchase #5	$183.38	9.236%	$200.317	$200.32	$200.30	$200.30
Purchase #6	$100.42	12.259%	$112.7305	$112.73	$112.75	$112.70
Purchase #7	$80.25	3.698%	$83.2176	$83.22	$83.20	$83.20
7 purchase totals =	$628.48		$679.9599	$679.97	$679.95	$679.90