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	$8.27	6.687%	$8.823	$8.82	$8.80	$8.80
Purchase #2	$51.91	11.337%	$57.795	$57.80	$57.80	$57.80
Purchase #3	$44.71	11.338%	$49.7792	$49.78	$49.80	$49.80
Purchase #4	$64.51	4.212%	$67.2272	$67.23	$67.25	$67.20
Purchase #5	$113.51	12.263%	$127.4297	$127.43	$127.45	$127.40
Purchase #6	$65.37	8.517%	$70.9376	$70.94	$70.95	$70.90
Purchase #7	$192.30	10.563%	$212.6126	$212.61	$212.60	$212.60
7 purchase totals =	$540.58		$594.6043	$594.61	$594.65	$594.50