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	$38.52	4.104%	$40.1009	$40.10	$40.10	$40.10
Purchase #2	$96.74	11.108%	$107.4859	$107.49	$107.50	$107.50
Purchase #3	$116.51	10.655%	$128.9241	$128.92	$128.90	$128.90
Purchase #4	$111.66	7.357%	$119.8748	$119.87	$119.85	$119.90
Purchase #5	$228.41	11.692%	$255.1157	$255.12	$255.10	$255.10
Purchase #6	$16.38	4.711%	$17.1517	$17.15	$17.15	$17.20
Purchase #7	$41.41	5.628%	$43.7406	$43.74	$43.75	$43.70
7 purchase totals =	$649.63		$712.3937	$712.39	$712.35	$712.40