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	$38.65	11.724%	$43.1813	$43.18	$43.20	$43.20
Purchase #2	$226.73	13.281%	$256.842	$256.84	$256.85	$256.80
Purchase #3	$23.86	3.451%	$24.6834	$24.68	$24.70	$24.70
Purchase #4	$131.47	11.326%	$146.3603	$146.36	$146.35	$146.40
Purchase #5	$86.45	6.492%	$92.0623	$92.06	$92.05	$92.10
Purchase #6	$73.55	13.172%	$83.238	$83.24	$83.25	$83.20
Purchase #7	$104.88	6.761%	$111.9709	$111.97	$111.95	$112.00
7 purchase totals =	$685.59		$758.3382	$758.33	$758.35	$758.40