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	$63.80	3.501%	$66.0336	$66.03	$66.05	$66.00
Purchase #2	$145.51	10.491%	$160.7755	$160.78	$160.80	$160.80
Purchase #3	$183.98	11.522%	$205.1782	$205.18	$205.20	$205.20
Purchase #4	$147.31	10.240%	$162.3945	$162.39	$162.40	$162.40
Purchase #5	$164.86	9.439%	$180.4211	$180.42	$180.40	$180.40
Purchase #6	$40.43	8.186%	$43.7396	$43.74	$43.75	$43.70
Purchase #7	$146.53	4.303%	$152.8352	$152.84	$152.85	$152.80
7 purchase totals =	$892.42		$971.3777	$971.38	$971.45	$971.30