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	$86.59	9.170%	$94.5303	$94.53	$94.55	$94.50
Purchase #2	$116.87	12.250%	$131.1866	$131.19	$131.20	$131.20
Purchase #3	$14.71	3.815%	$15.2712	$15.27	$15.25	$15.30
Purchase #4	$128.52	7.848%	$138.6062	$138.61	$138.60	$138.60
Purchase #5	$185.45	12.128%	$207.9414	$207.94	$207.95	$207.90
Purchase #6	$133.63	8.773%	$145.3534	$145.35	$145.35	$145.40
Purchase #7	$101.27	4.284%	$105.6084	$105.61	$105.60	$105.60
7 purchase totals =	$767.04		$838.4975	$838.50	$838.50	$838.50