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	$85.71	4.443%	$89.5181	$89.52	$89.50	$89.50
Purchase #2	$36.30	7.727%	$39.1049	$39.10	$39.10	$39.10
Purchase #3	$165.43	5.462%	$174.4658	$174.47	$174.45	$174.50
Purchase #4	$226.59	13.357%	$256.8556	$256.86	$256.85	$256.90
Purchase #5	$179.67	13.230%	$203.4403	$203.44	$203.45	$203.40
Purchase #6	$122.53	6.245%	$130.182	$130.18	$130.20	$130.20
Purchase #7	$158.61	12.491%	$178.422	$178.42	$178.40	$178.40
7 purchase totals =	$974.84		$1,071.9887	$1,071.99	$1,071.95	$1,072.00