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	$11.59	13.307%	$13.1323	$13.13	$13.15	$13.10
Purchase #2	$111.59	4.501%	$116.6127	$116.61	$116.60	$116.60
Purchase #3	$216.55	3.768%	$224.7096	$224.71	$224.70	$224.70
Purchase #4	$70.78	9.439%	$77.4609	$77.46	$77.45	$77.50
Purchase #5	$58.43	11.730%	$65.2838	$65.28	$65.30	$65.30
Purchase #6	$245.97	8.164%	$266.051	$266.05	$266.05	$266.10
Purchase #7	$109.41	3.792%	$113.5588	$113.56	$113.55	$113.60
7 purchase totals =	$824.32		$876.8091	$876.80	$876.80	$876.90