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	$223.63	5.212%	$235.2856	$235.29	$235.30	$235.30
Purchase #2	$137.50	12.325%	$154.4469	$154.45	$154.45	$154.40
Purchase #3	$77.49	8.195%	$83.8403	$83.84	$83.85	$83.80
Purchase #4	$9.34	13.323%	$10.5844	$10.58	$10.60	$10.60
Purchase #5	$27.90	11.534%	$31.118	$31.12	$31.10	$31.10
Purchase #6	$64.98	11.409%	$72.3936	$72.39	$72.40	$72.40
Purchase #7	$14.76	3.461%	$15.2708	$15.27	$15.25	$15.30
7 purchase totals =	$555.60		$602.9396	$602.94	$602.95	$602.90