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	$232.28	12.526%	$261.3754	$261.38	$261.40	$261.40
Purchase #2	$50.39	3.777%	$52.2932	$52.29	$52.30	$52.30
Purchase #3	$111.44	4.643%	$116.6142	$116.61	$116.60	$116.60
Purchase #4	$32.28	5.497%	$34.0544	$34.05	$34.05	$34.10
Purchase #5	$155.54	5.860%	$164.6546	$164.65	$164.65	$164.70
Purchase #6	$91.81	9.419%	$100.4576	$100.46	$100.45	$100.50
Purchase #7	$46.86	3.465%	$48.4837	$48.48	$48.50	$48.50
7 purchase totals =	$720.60		$777.9331	$777.92	$777.95	$778.10