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	$38.32	6.442%	$40.7886	$40.79	$40.80	$40.80
Purchase #2	$45.94	6.343%	$48.854	$48.85	$48.85	$48.90
Purchase #3	$111.93	11.340%	$124.6229	$124.62	$124.60	$124.60
Purchase #4	$160.53	12.864%	$181.1806	$181.18	$181.20	$181.20
Purchase #5	$13.51	9.205%	$14.7536	$14.75	$14.75	$14.80
Purchase #6	$118.47	4.714%	$124.0547	$124.05	$124.05	$124.10
Purchase #7	$101.65	9.333%	$111.137	$111.14	$111.15	$111.10
7 purchase totals =	$590.35		$645.3914	$645.38	$645.40	$645.50