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	$241.59	11.143%	$268.5104	$268.51	$268.50	$268.50
Purchase #2	$155.39	11.188%	$172.775	$172.78	$172.80	$172.80
Purchase #3	$162.54	10.575%	$179.7286	$179.73	$179.75	$179.70
Purchase #4	$175.55	6.548%	$187.045	$187.05	$187.05	$187.00
Purchase #5	$52.48	4.642%	$54.9161	$54.92	$54.90	$54.90
Purchase #6	$185.69	12.698%	$209.2689	$209.27	$209.25	$209.30
Purchase #7	$116.84	9.409%	$127.8335	$127.83	$127.85	$127.80
7 purchase totals =	$1,090.08		$1,200.0775	$1,200.09	$1,200.10	$1,200.00