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	$86.55	4.417%	$90.3729	$90.37	$90.35	$90.40
Purchase #2	$64.60	9.312%	$70.6156	$70.62	$70.60	$70.60
Purchase #3	$60.25	13.769%	$68.5458	$68.55	$68.55	$68.50
Purchase #4	$141.83	10.169%	$156.2527	$156.25	$156.25	$156.30
Purchase #5	$127.39	8.439%	$138.1404	$138.14	$138.15	$138.10
Purchase #6	$41.84	9.791%	$45.9366	$45.94	$45.95	$45.90
Purchase #7	$106.36	6.448%	$113.2181	$113.22	$113.20	$113.20
7 purchase totals =	$628.82		$683.0821	$683.09	$683.05	$683.00