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	$100.32	12.352%	$112.7115	$112.71	$112.70	$112.70
Purchase #2	$31.96	8.266%	$34.6018	$34.60	$34.60	$34.60
Purchase #3	$134.91	13.745%	$153.4534	$153.45	$153.45	$153.50
Purchase #4	$118.42	4.103%	$123.2788	$123.28	$123.30	$123.30
Purchase #5	$83.40	6.796%	$89.0679	$89.07	$89.05	$89.10
Purchase #6	$67.33	12.698%	$75.8796	$75.88	$75.90	$75.90
Purchase #7	$128.46	7.763%	$138.4323	$138.43	$138.45	$138.40
7 purchase totals =	$664.80		$727.4253	$727.42	$727.45	$727.50