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	$18.84	4.131%	$19.6183	$19.62	$19.60	$19.60
Purchase #2	$72.86	8.194%	$78.8301	$78.83	$78.85	$78.80
Purchase #3	$11.53	3.572%	$11.9419	$11.94	$11.95	$11.90
Purchase #4	$153.49	9.704%	$168.3847	$168.38	$168.40	$168.40
Purchase #5	$242.43	13.561%	$275.3059	$275.31	$275.30	$275.30
Purchase #6	$169.52	12.517%	$190.7388	$190.74	$190.75	$190.70
Purchase #7	$82.76	11.742%	$92.4777	$92.48	$92.50	$92.50
7 purchase totals =	$751.43		$837.2974	$837.30	$837.35	$837.20