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	$18.42	10.583%	$20.3694	$20.37	$20.35	$20.40
Purchase #2	$64.47	4.662%	$67.4756	$67.48	$67.50	$67.50
Purchase #3	$139.55	4.181%	$145.3846	$145.38	$145.40	$145.40
Purchase #4	$59.85	13.833%	$68.1291	$68.13	$68.15	$68.10
Purchase #5	$95.69	13.372%	$108.4857	$108.49	$108.50	$108.50
Purchase #6	$9.62	7.230%	$10.3155	$10.32	$10.30	$10.30
Purchase #7	$159.44	12.622%	$179.5645	$179.56	$179.55	$179.60
7 purchase totals =	$547.04		$599.7244	$599.73	$599.75	$599.80