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	$129.82	10.727%	$143.7458	$143.75	$143.75	$143.70
Purchase #2	$143.64	12.526%	$161.6323	$161.63	$161.65	$161.60
Purchase #3	$55.26	4.754%	$57.8871	$57.89	$57.90	$57.90
Purchase #4	$213.91	3.525%	$221.4503	$221.45	$221.45	$221.50
Purchase #5	$89.82	9.300%	$98.1733	$98.17	$98.15	$98.20
Purchase #6	$50.58	4.356%	$52.7833	$52.78	$52.80	$52.80
Purchase #7	$59.32	10.612%	$65.615	$65.62	$65.60	$65.60
7 purchase totals =	$742.35		$801.2871	$801.29	$801.30	$801.30