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	$48.30	6.321%	$51.353	$51.35	$51.35	$51.40
Purchase #2	$140.45	12.480%	$157.9782	$157.98	$158.00	$158.00
Purchase #3	$18.72	10.642%	$20.7122	$20.71	$20.70	$20.70
Purchase #4	$210.33	12.571%	$236.7706	$236.77	$236.75	$236.80
Purchase #5	$34.38	10.754%	$38.0772	$38.08	$38.10	$38.10
Purchase #6	$146.93	5.375%	$154.8275	$154.83	$154.85	$154.80
Purchase #7	$55.81	6.817%	$59.6146	$59.61	$59.60	$59.60
7 purchase totals =	$654.92		$719.3333	$719.33	$719.35	$719.40