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	$146.79	7.837%	$158.2939	$158.29	$158.30	$158.30
Purchase #2	$102.95	12.508%	$115.827	$115.83	$115.85	$115.80
Purchase #3	$36.72	13.619%	$41.7209	$41.72	$41.70	$41.70
Purchase #4	$10.57	10.177%	$11.6457	$11.65	$11.65	$11.60
Purchase #5	$100.78	10.815%	$111.6794	$111.68	$111.70	$111.70
Purchase #6	$39.27	4.260%	$40.9429	$40.94	$40.95	$40.90
Purchase #7	$83.91	13.286%	$95.0583	$95.06	$95.05	$95.10
7 purchase totals =	$520.99		$575.1681	$575.17	$575.20	$575.10