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	$71.72	9.212%	$78.3268	$78.33	$78.35	$78.30
Purchase #2	$48.28	11.417%	$53.7921	$53.79	$53.80	$53.80
Purchase #3	$121.83	12.104%	$136.5763	$136.58	$136.60	$136.60
Purchase #4	$12.72	8.338%	$13.7806	$13.78	$13.80	$13.80
Purchase #5	$37.52	4.479%	$39.2005	$39.20	$39.20	$39.20
Purchase #6	$240.81	8.107%	$260.3325	$260.33	$260.35	$260.30
Purchase #7	$37.45	10.859%	$41.5167	$41.52	$41.50	$41.50
7 purchase totals =	$570.33		$623.5255	$623.53	$623.60	$623.50