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	$239.57	3.582%	$248.1514	$248.15	$248.15	$248.20
Purchase #2	$88.29	9.544%	$96.7164	$96.72	$96.70	$96.70
Purchase #3	$87.40	10.771%	$96.8139	$96.81	$96.80	$96.80
Purchase #4	$105.83	13.485%	$120.1012	$120.10	$120.10	$120.10
Purchase #5	$105.69	5.508%	$111.5114	$111.51	$111.50	$111.50
Purchase #6	$230.46	7.117%	$246.8618	$246.86	$246.85	$246.90
Purchase #7	$97.89	11.723%	$109.3656	$109.37	$109.35	$109.40
7 purchase totals =	$955.13		$1,029.5217	$1,029.52	$1,029.45	$1,029.60