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	$17.89	8.137%	$19.3457	$19.35	$19.35	$19.30
Purchase #2	$191.82	10.590%	$212.1337	$212.13	$212.15	$212.10
Purchase #3	$111.33	6.729%	$118.8214	$118.82	$118.80	$118.80
Purchase #4	$137.93	3.752%	$143.1051	$143.11	$143.10	$143.10
Purchase #5	$132.44	4.111%	$137.8846	$137.88	$137.90	$137.90
Purchase #6	$10.57	5.733%	$11.176	$11.18	$11.20	$11.20
Purchase #7	$124.33	8.184%	$134.5052	$134.51	$134.50	$134.50
7 purchase totals =	$726.31		$776.9717	$776.98	$777.00	$776.90