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	$99.52	3.636%	$103.1385	$103.14	$103.15	$103.10
Purchase #2	$131.97	8.660%	$143.3986	$143.40	$143.40	$143.40
Purchase #3	$10.38	9.647%	$11.3814	$11.38	$11.40	$11.40
Purchase #4	$47.26	6.110%	$50.1476	$50.15	$50.15	$50.10
Purchase #5	$20.83	3.712%	$21.6032	$21.60	$21.60	$21.60
Purchase #6	$151.38	10.773%	$167.6882	$167.69	$167.70	$167.70
Purchase #7	$173.61	12.363%	$195.0734	$195.07	$195.05	$195.10
7 purchase totals =	$634.95		$692.4309	$692.43	$692.45	$692.40