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	$37.51	12.346%	$42.141	$42.14	$42.15	$42.10
Purchase #2	$9.69	13.267%	$10.9756	$10.98	$11.00	$11.00
Purchase #3	$99.43	5.710%	$105.1075	$105.11	$105.10	$105.10
Purchase #4	$69.97	7.692%	$75.3521	$75.35	$75.35	$75.40
Purchase #5	$103.38	8.286%	$111.9461	$111.95	$111.95	$111.90
Purchase #6	$77.44	9.873%	$85.0857	$85.09	$85.10	$85.10
Purchase #7	$136.29	12.230%	$152.9583	$152.96	$152.95	$153.00
7 purchase totals =	$533.71		$583.5663	$583.58	$583.60	$583.60