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	$37.37	7.873%	$40.3121	$40.31	$40.30	$40.30
Purchase #2	$26.43	4.121%	$27.5192	$27.52	$27.50	$27.50
Purchase #3	$111.91	4.252%	$116.6684	$116.67	$116.65	$116.70
Purchase #4	$11.27	7.615%	$12.1282	$12.13	$12.15	$12.10
Purchase #5	$236.75	12.102%	$265.4015	$265.40	$265.40	$265.40
Purchase #6	$112.69	12.105%	$126.3311	$126.33	$126.35	$126.30
Purchase #7	$107.74	8.406%	$116.7966	$116.80	$116.80	$116.80
7 purchase totals =	$644.16		$705.1571	$705.16	$705.15	$705.10