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	$37.68	7.578%	$40.5354	$40.54	$40.55	$40.50
Purchase #2	$94.81	5.753%	$100.2644	$100.26	$100.25	$100.30
Purchase #3	$18.46	4.559%	$19.3016	$19.30	$19.30	$19.30
Purchase #4	$51.85	4.475%	$54.1703	$54.17	$54.15	$54.20
Purchase #5	$105.48	5.462%	$111.2413	$111.24	$111.25	$111.20
Purchase #6	$220.44	7.789%	$237.6101	$237.61	$237.60	$237.60
Purchase #7	$219.46	10.651%	$242.8347	$242.83	$242.85	$242.80
7 purchase totals =	$748.18		$805.9578	$805.95	$805.95	$805.90