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	$9.86	7.396%	$10.5892	$10.59	$10.60	$10.60
Purchase #2	$171.47	4.722%	$179.5668	$179.57	$179.55	$179.60
Purchase #3	$214.83	12.390%	$241.4474	$241.45	$241.45	$241.40
Purchase #4	$219.68	10.526%	$242.8035	$242.80	$242.80	$242.80
Purchase #5	$117.85	11.658%	$131.589	$131.59	$131.60	$131.60
Purchase #6	$242.98	3.740%	$252.0675	$252.07	$252.05	$252.10
Purchase #7	$132.75	7.554%	$142.7779	$142.78	$142.80	$142.80
7 purchase totals =	$1,109.42		$1,200.8413	$1,200.85	$1,200.85	$1,200.90