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	$245.69	4.221%	$256.0606	$256.06	$256.05	$256.10
Purchase #2	$180.38	10.493%	$199.3073	$199.31	$199.30	$199.30
Purchase #3	$220.59	13.868%	$251.1814	$251.18	$251.20	$251.20
Purchase #4	$128.38	9.223%	$140.2205	$140.22	$140.20	$140.20
Purchase #5	$95.83	10.540%	$105.9305	$105.93	$105.95	$105.90
Purchase #6	$224.28	7.640%	$241.415	$241.42	$241.40	$241.40
Purchase #7	$249.78	13.227%	$282.8184	$282.82	$282.80	$282.80
7 purchase totals =	$1,344.93		$1,476.9337	$1,476.94	$1,476.90	$1,476.90