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	$17.61	12.602%	$19.8292	$19.83	$19.85	$19.80
Purchase #2	$243.35	12.808%	$274.5183	$274.52	$274.50	$274.50
Purchase #3	$115.57	13.631%	$131.3233	$131.32	$131.30	$131.30
Purchase #4	$230.68	3.817%	$239.4851	$239.49	$239.50	$239.50
Purchase #5	$51.32	5.182%	$53.9794	$53.98	$54.00	$54.00
Purchase #6	$172.77	10.477%	$190.8711	$190.87	$190.85	$190.90
Purchase #7	$145.39	13.762%	$165.3986	$165.40	$165.40	$165.40
7 purchase totals =	$976.69		$1,075.4050	$1,075.41	$1,075.40	$1,075.40