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	$166.31	12.608%	$187.2784	$187.28	$187.30	$187.30
Purchase #2	$22.48	12.395%	$25.2664	$25.27	$25.25	$25.30
Purchase #3	$111.27	11.422%	$123.9793	$123.98	$124.00	$124.00
Purchase #4	$59.83	10.206%	$65.9362	$65.94	$65.95	$65.90
Purchase #5	$39.32	10.461%	$43.4333	$43.43	$43.45	$43.40
Purchase #6	$241.52	5.417%	$254.6031	$254.60	$254.60	$254.60
Purchase #7	$123.25	8.326%	$133.5118	$133.51	$133.50	$133.50
7 purchase totals =	$763.98		$834.0085	$834.01	$834.05	$834.00