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	$30.87	9.705%	$33.8659	$33.87	$33.85	$33.90
Purchase #2	$88.61	13.242%	$100.3437	$100.34	$100.35	$100.30
Purchase #3	$192.41	4.188%	$200.4681	$200.47	$200.45	$200.50
Purchase #4	$118.30	8.754%	$128.656	$128.66	$128.65	$128.70
Purchase #5	$74.56	9.128%	$81.3658	$81.37	$81.35	$81.40
Purchase #6	$222.28	3.870%	$230.8822	$230.88	$230.90	$230.90
Purchase #7	$136.40	6.717%	$145.562	$145.56	$145.55	$145.60
7 purchase totals =	$863.43		$921.1437	$921.15	$921.10	$921.30