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	$92.27	9.336%	$100.8843	$100.88	$100.90	$100.90
Purchase #2	$97.93	13.541%	$111.1907	$111.19	$111.20	$111.20
Purchase #3	$41.49	4.723%	$43.4496	$43.45	$43.45	$43.40
Purchase #4	$75.50	8.652%	$82.0323	$82.03	$82.05	$82.00
Purchase #5	$153.84	3.122%	$158.6429	$158.64	$158.65	$158.60
Purchase #6	$198.78	3.671%	$206.0772	$206.08	$206.10	$206.10
Purchase #7	$122.41	4.522%	$127.9454	$127.95	$127.95	$127.90
7 purchase totals =	$782.22		$830.2224	$830.22	$830.30	$830.10