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	$127.93	8.179%	$138.3934	$138.39	$138.40	$138.40
Purchase #2	$90.85	7.228%	$97.4166	$97.42	$97.40	$97.40
Purchase #3	$44.77	11.871%	$50.0846	$50.08	$50.10	$50.10
Purchase #4	$10.58	5.680%	$11.1809	$11.18	$11.20	$11.20
Purchase #5	$66.80	5.818%	$70.6864	$70.69	$70.70	$70.70
Purchase #6	$118.47	4.219%	$123.4682	$123.47	$123.45	$123.50
Purchase #7	$36.30	13.188%	$41.0872	$41.09	$41.10	$41.10
7 purchase totals =	$495.70		$532.3173	$532.32	$532.35	$532.40