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	$166.36	10.270%	$183.4452	$183.45	$183.45	$183.40
Purchase #2	$155.78	11.440%	$173.6012	$173.60	$173.60	$173.60
Purchase #3	$80.83	12.339%	$90.8036	$90.80	$90.80	$90.80
Purchase #4	$145.92	6.860%	$155.9301	$155.93	$155.95	$155.90
Purchase #5	$16.70	12.269%	$18.7489	$18.75	$18.75	$18.70
Purchase #6	$242.39	12.307%	$272.2209	$272.22	$272.20	$272.20
Purchase #7	$122.33	13.577%	$138.9387	$138.94	$138.95	$138.90
7 purchase totals =	$930.31		$1,033.6886	$1,033.69	$1,033.70	$1,033.50