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	$101.78	9.208%	$111.1519	$111.15	$111.15	$111.20
Purchase #2	$89.30	3.605%	$92.5193	$92.52	$92.50	$92.50
Purchase #3	$90.50	11.776%	$101.1573	$101.16	$101.15	$101.20
Purchase #4	$121.60	4.442%	$127.0015	$127.00	$127.00	$127.00
Purchase #5	$53.51	3.667%	$55.4722	$55.47	$55.45	$55.50
Purchase #6	$42.81	7.745%	$46.1256	$46.13	$46.15	$46.10
Purchase #7	$51.93	4.238%	$54.1308	$54.13	$54.15	$54.10
7 purchase totals =	$551.43		$587.5586	$587.56	$587.55	$587.60