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	$155.45	7.113%	$166.5072	$166.51	$166.50	$166.50
Purchase #2	$105.30	10.436%	$116.2891	$116.29	$116.30	$116.30
Purchase #3	$70.49	11.174%	$78.3666	$78.37	$78.35	$78.40
Purchase #4	$77.80	3.742%	$80.7113	$80.71	$80.70	$80.70
Purchase #5	$167.67	5.146%	$176.2983	$176.30	$176.30	$176.30
Purchase #6	$57.93	12.207%	$65.0015	$65.00	$65.00	$65.00
Purchase #7	$46.26	4.440%	$48.3139	$48.31	$48.30	$48.30
7 purchase totals =	$680.90		$731.4879	$731.49	$731.45	$731.50