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	$36.28	4.126%	$37.7769	$37.78	$37.80	$37.80
Purchase #2	$97.92	5.654%	$103.4564	$103.46	$103.45	$103.50
Purchase #3	$155.35	11.811%	$173.6984	$173.70	$173.70	$173.70
Purchase #4	$15.82	12.178%	$17.7466	$17.75	$17.75	$17.70
Purchase #5	$66.98	8.322%	$72.5541	$72.55	$72.55	$72.60
Purchase #6	$19.84	7.860%	$21.3994	$21.40	$21.40	$21.40
Purchase #7	$143.83	4.685%	$150.5684	$150.57	$150.55	$150.60
7 purchase totals =	$536.02		$577.2002	$577.21	$577.20	$577.30