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	$90.90	12.360%	$102.1352	$102.14	$102.15	$102.10
Purchase #2	$136.43	4.752%	$142.9132	$142.91	$142.90	$142.90
Purchase #3	$83.90	11.826%	$93.822	$93.82	$93.80	$93.80
Purchase #4	$160.26	9.846%	$176.0392	$176.04	$176.05	$176.00
Purchase #5	$247.53	10.231%	$272.8548	$272.85	$272.85	$272.90
Purchase #6	$66.60	5.794%	$70.4588	$70.46	$70.45	$70.50
Purchase #7	$230.93	3.244%	$238.4214	$238.42	$238.40	$238.40
7 purchase totals =	$1,016.55		$1,096.6446	$1,096.64	$1,096.60	$1,096.60