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	$245.36	13.752%	$279.1019	$279.10	$279.10	$279.10
Purchase #2	$129.83	10.837%	$143.8997	$143.90	$143.90	$143.90
Purchase #3	$142.36	12.370%	$159.9699	$159.97	$159.95	$160.00
Purchase #4	$28.92	9.476%	$31.6605	$31.66	$31.65	$31.70
Purchase #5	$149.39	6.162%	$158.5954	$158.60	$158.60	$158.60
Purchase #6	$146.32	4.144%	$152.3835	$152.38	$152.40	$152.40
Purchase #7	$34.83	6.235%	$37.0017	$37.00	$37.00	$37.00
7 purchase totals =	$877.01		$962.6126	$962.61	$962.60	$962.70