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	$82.82	9.296%	$90.5189	$90.52	$90.50	$90.50
Purchase #2	$49.35	8.852%	$53.7185	$53.72	$53.70	$53.70
Purchase #3	$40.46	7.155%	$43.3549	$43.35	$43.35	$43.40
Purchase #4	$58.69	12.624%	$66.099	$66.10	$66.10	$66.10
Purchase #5	$69.43	11.778%	$77.6075	$77.61	$77.60	$77.60
Purchase #6	$177.70	6.148%	$188.625	$188.63	$188.65	$188.60
Purchase #7	$166.87	3.136%	$172.103	$172.10	$172.10	$172.10
7 purchase totals =	$645.32		$692.0268	$692.03	$692.00	$692.00