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	$49.72	9.461%	$54.424	$54.42	$54.40	$54.40
Purchase #2	$184.66	5.338%	$194.5172	$194.52	$194.50	$194.50
Purchase #3	$50.66	3.247%	$52.3049	$52.30	$52.30	$52.30
Purchase #4	$57.87	7.809%	$62.3891	$62.39	$62.40	$62.40
Purchase #5	$136.72	3.747%	$141.8429	$141.84	$141.85	$141.80
Purchase #6	$37.99	8.569%	$41.2454	$41.25	$41.25	$41.20
Purchase #7	$130.57	11.271%	$145.2865	$145.29	$145.30	$145.30
7 purchase totals =	$648.19		$692.0100	$692.01	$692.00	$691.90