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	$15.25	8.172%	$16.4962	$16.50	$16.50	$16.50
Purchase #2	$241.84	5.563%	$255.2936	$255.29	$255.30	$255.30
Purchase #3	$230.41	5.664%	$243.4604	$243.46	$243.45	$243.50
Purchase #4	$172.41	6.382%	$183.4132	$183.41	$183.40	$183.40
Purchase #5	$167.85	10.608%	$185.6555	$185.66	$185.65	$185.70
Purchase #6	$188.45	6.588%	$200.8651	$200.87	$200.85	$200.90
Purchase #7	$73.88	13.406%	$83.7844	$83.78	$83.80	$83.80
7 purchase totals =	$1,090.09		$1,168.9684	$1,168.97	$1,168.95	$1,169.10