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	$29.80	4.328%	$31.0897	$31.09	$31.10	$31.10
Purchase #2	$204.68	9.589%	$224.3068	$224.31	$224.30	$224.30
Purchase #3	$157.33	10.458%	$173.7836	$173.78	$173.80	$173.80
Purchase #4	$99.45	3.626%	$103.0561	$103.06	$103.05	$103.10
Purchase #5	$128.86	12.653%	$145.1647	$145.16	$145.15	$145.20
Purchase #6	$217.56	9.674%	$238.6068	$238.61	$238.60	$238.60
Purchase #7	$160.86	12.822%	$181.4855	$181.49	$181.50	$181.50
7 purchase totals =	$998.54		$1,097.4932	$1,097.50	$1,097.50	$1,097.60