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	$138.64	8.780%	$150.8126	$150.81	$150.80	$150.80
Purchase #2	$234.89	4.810%	$246.1882	$246.19	$246.20	$246.20
Purchase #3	$224.45	10.521%	$248.0644	$248.06	$248.05	$248.10
Purchase #4	$241.38	13.577%	$274.1522	$274.15	$274.15	$274.20
Purchase #5	$102.91	8.424%	$111.5791	$111.58	$111.60	$111.60
Purchase #6	$35.76	8.675%	$38.8622	$38.86	$38.85	$38.90
Purchase #7	$162.47	6.594%	$173.1833	$173.18	$173.20	$173.20
7 purchase totals =	$1,140.50		$1,242.8420	$1,242.83	$1,242.85	$1,243.00