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	$101.51	5.556%	$107.1499	$107.15	$107.15	$107.10
Purchase #2	$216.70	5.488%	$228.5925	$228.59	$228.60	$228.60
Purchase #3	$104.53	12.287%	$117.3736	$117.37	$117.35	$117.40
Purchase #4	$186.47	10.137%	$205.3725	$205.37	$205.35	$205.40
Purchase #5	$226.77	13.113%	$256.5064	$256.51	$256.50	$256.50
Purchase #6	$229.81	10.318%	$253.5218	$253.52	$253.50	$253.50
Purchase #7	$116.93	11.479%	$130.3524	$130.35	$130.35	$130.40
7 purchase totals =	$1,182.72		$1,298.8691	$1,298.86	$1,298.80	$1,298.90