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	$63.47	3.286%	$65.5556	$65.56	$65.55	$65.60
Purchase #2	$192.39	12.677%	$216.7793	$216.78	$216.80	$216.80
Purchase #3	$138.32	9.731%	$151.7799	$151.78	$151.80	$151.80
Purchase #4	$18.95	7.238%	$20.3216	$20.32	$20.30	$20.30
Purchase #5	$211.97	13.807%	$241.2367	$241.24	$241.25	$241.20
Purchase #6	$108.40	5.828%	$114.7176	$114.72	$114.70	$114.70
Purchase #7	$234.31	10.719%	$259.4257	$259.43	$259.45	$259.40
7 purchase totals =	$967.81		$1,069.8164	$1,069.83	$1,069.85	$1,069.80