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	$250.55	8.719%	$272.3955	$272.40	$272.40	$272.40
Purchase #2	$199.35	9.657%	$218.6012	$218.60	$218.60	$218.60
Purchase #3	$81.82	10.184%	$90.1525	$90.15	$90.15	$90.20
Purchase #4	$128.32	11.681%	$143.3091	$143.31	$143.30	$143.30
Purchase #5	$85.27	3.659%	$88.39	$88.39	$88.40	$88.40
Purchase #6	$214.58	6.233%	$227.9548	$227.95	$227.95	$228.00
Purchase #7	$126.53	3.372%	$130.7966	$130.80	$130.80	$130.80
7 purchase totals =	$1,086.42		$1,171.5997	$1,171.60	$1,171.60	$1,171.70