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	$241.85	12.440%	$271.9361	$271.94	$271.95	$271.90
Purchase #2	$107.72	6.320%	$114.5279	$114.53	$114.55	$114.50
Purchase #3	$250.95	9.622%	$275.0964	$275.10	$275.10	$275.10
Purchase #4	$162.72	10.218%	$179.3467	$179.35	$179.35	$179.30
Purchase #5	$59.34	11.492%	$66.1594	$66.16	$66.15	$66.20
Purchase #6	$120.52	11.561%	$134.4533	$134.45	$134.45	$134.50
Purchase #7	$108.92	13.542%	$123.6699	$123.67	$123.65	$123.70
7 purchase totals =	$1,052.02		$1,165.1897	$1,165.20	$1,165.20	$1,165.20