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	$109.92	12.287%	$123.4259	$123.43	$123.45	$123.40
Purchase #2	$237.64	7.178%	$254.6978	$254.70	$254.70	$254.70
Purchase #3	$38.30	3.720%	$39.7248	$39.72	$39.70	$39.70
Purchase #4	$10.76	12.433%	$12.0978	$12.10	$12.10	$12.10
Purchase #5	$238.82	9.740%	$262.0811	$262.08	$262.10	$262.10
Purchase #6	$75.56	9.142%	$82.4677	$82.47	$82.45	$82.50
Purchase #7	$152.40	4.732%	$159.6116	$159.61	$159.60	$159.60
7 purchase totals =	$863.40		$934.1067	$934.11	$934.10	$934.10