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	$104.81	13.281%	$118.7298	$118.73	$118.75	$118.70
Purchase #2	$48.69	7.862%	$52.518	$52.52	$52.50	$52.50
Purchase #3	$248.52	12.303%	$279.0954	$279.10	$279.10	$279.10
Purchase #4	$158.49	13.539%	$179.948	$179.95	$179.95	$179.90
Purchase #5	$145.52	5.427%	$153.4174	$153.42	$153.40	$153.40
Purchase #6	$135.45	4.509%	$141.5574	$141.56	$141.55	$141.60
Purchase #7	$76.66	8.766%	$83.38	$83.38	$83.40	$83.40
7 purchase totals =	$918.14		$1,008.6460	$1,008.66	$1,008.65	$1,008.60