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	$133.93	4.459%	$139.9019	$139.90	$139.90	$139.90
Purchase #2	$27.40	6.712%	$29.2391	$29.24	$29.25	$29.20
Purchase #3	$112.82	13.262%	$127.7822	$127.78	$127.80	$127.80
Purchase #4	$156.39	5.689%	$165.287	$165.29	$165.30	$165.30
Purchase #5	$42.86	6.784%	$45.7676	$45.77	$45.75	$45.80
Purchase #6	$101.62	8.708%	$110.4691	$110.47	$110.45	$110.50
Purchase #7	$205.89	4.246%	$214.6321	$214.63	$214.65	$214.60
7 purchase totals =	$780.91		$833.0790	$833.08	$833.10	$833.10