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	$133.61	4.712%	$139.9057	$139.91	$139.90	$139.90
Purchase #2	$81.96	9.239%	$89.5323	$89.53	$89.55	$89.50
Purchase #3	$87.71	13.273%	$99.3517	$99.35	$99.35	$99.40
Purchase #4	$12.68	4.864%	$13.2968	$13.30	$13.30	$13.30
Purchase #5	$15.37	12.414%	$17.278	$17.28	$17.30	$17.30
Purchase #6	$234.52	13.456%	$266.077	$266.08	$266.10	$266.10
Purchase #7	$25.57	13.625%	$29.0539	$29.05	$29.05	$29.10
7 purchase totals =	$591.42		$654.4954	$654.50	$654.55	$654.60