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	$155.31	10.786%	$172.0617	$172.06	$172.05	$172.10
Purchase #2	$202.42	12.202%	$227.1193	$227.12	$227.10	$227.10
Purchase #3	$37.34	13.142%	$42.2472	$42.25	$42.25	$42.20
Purchase #4	$31.53	7.747%	$33.9726	$33.97	$33.95	$34.00
Purchase #5	$6.32	6.836%	$6.752	$6.75	$6.75	$6.80
Purchase #6	$22.26	11.727%	$24.8704	$24.87	$24.85	$24.90
Purchase #7	$129.70	11.371%	$144.4482	$144.45	$144.45	$144.40
7 purchase totals =	$584.88		$651.4714	$651.47	$651.40	$651.50