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	$122.27	4.213%	$127.4212	$127.42	$127.40	$127.40
Purchase #2	$41.63	8.245%	$45.0624	$45.06	$45.05	$45.10
Purchase #3	$10.93	8.437%	$11.8522	$11.85	$11.85	$11.90
Purchase #4	$78.55	13.664%	$89.2831	$89.28	$89.30	$89.30
Purchase #5	$157.47	9.845%	$172.9729	$172.97	$172.95	$173.00
Purchase #6	$182.86	4.495%	$191.0796	$191.08	$191.10	$191.10
Purchase #7	$189.92	12.744%	$214.1234	$214.12	$214.10	$214.10
7 purchase totals =	$783.63		$851.7948	$851.78	$851.75	$851.90