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	$58.32	13.243%	$66.0433	$66.04	$66.05	$66.00
Purchase #2	$14.60	6.469%	$15.5445	$15.54	$15.55	$15.50
Purchase #3	$78.34	13.868%	$89.2042	$89.20	$89.20	$89.20
Purchase #4	$13.28	12.809%	$14.981	$14.98	$15.00	$15.00
Purchase #5	$126.79	3.624%	$131.3849	$131.38	$131.40	$131.40
Purchase #6	$193.61	5.866%	$204.9672	$204.97	$204.95	$205.00
Purchase #7	$127.52	12.288%	$143.1897	$143.19	$143.20	$143.20
7 purchase totals =	$612.46		$665.3148	$665.30	$665.35	$665.30