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	$31.50	6.652%	$33.5954	$33.60	$33.60	$33.60
Purchase #2	$176.94	11.388%	$197.0899	$197.09	$197.10	$197.10
Purchase #3	$35.81	4.353%	$37.3688	$37.37	$37.35	$37.40
Purchase #4	$77.71	7.367%	$83.4349	$83.43	$83.45	$83.40
Purchase #5	$62.43	6.232%	$66.3206	$66.32	$66.30	$66.30
Purchase #6	$5.87	3.353%	$6.0668	$6.07	$6.05	$6.10
Purchase #7	$82.48	10.111%	$90.8196	$90.82	$90.80	$90.80
7 purchase totals =	$472.74		$514.6960	$514.70	$514.65	$514.70