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	$241.45	11.170%	$268.42	$268.42	$268.40	$268.40
Purchase #2	$39.83	10.275%	$43.9225	$43.92	$43.90	$43.90
Purchase #3	$160.48	13.158%	$181.596	$181.60	$181.60	$181.60
Purchase #4	$140.34	13.271%	$158.9645	$158.96	$158.95	$159.00
Purchase #5	$112.26	13.314%	$127.2063	$127.21	$127.20	$127.20
Purchase #6	$27.44	7.608%	$29.5276	$29.53	$29.55	$29.50
Purchase #7	$66.49	12.579%	$74.8538	$74.85	$74.85	$74.90
7 purchase totals =	$788.29		$884.4907	$884.49	$884.45	$884.50