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	$11.56	11.230%	$12.8582	$12.86	$12.85	$12.90
Purchase #2	$80.35	10.243%	$88.5803	$88.58	$88.60	$88.60
Purchase #3	$65.40	3.195%	$67.4895	$67.49	$67.50	$67.50
Purchase #4	$121.77	13.200%	$137.8436	$137.84	$137.85	$137.80
Purchase #5	$145.46	6.157%	$154.416	$154.42	$154.40	$154.40
Purchase #6	$176.78	13.378%	$200.4296	$200.43	$200.45	$200.40
Purchase #7	$45.91	13.211%	$51.9752	$51.98	$52.00	$52.00
7 purchase totals =	$647.23		$713.5924	$713.60	$713.65	$713.60