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	$159.61	8.766%	$173.6014	$173.60	$173.60	$173.60
Purchase #2	$40.82	5.517%	$43.072	$43.07	$43.05	$43.10
Purchase #3	$126.48	3.656%	$131.1041	$131.10	$131.10	$131.10
Purchase #4	$164.95	13.137%	$186.6195	$186.62	$186.60	$186.60
Purchase #5	$191.93	10.675%	$212.4185	$212.42	$212.40	$212.40
Purchase #6	$36.94	8.753%	$40.1734	$40.17	$40.15	$40.20
Purchase #7	$14.32	8.218%	$15.4968	$15.50	$15.50	$15.50
7 purchase totals =	$735.05		$802.4857	$802.48	$802.40	$802.50