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	$11.48	11.339%	$12.7817	$12.78	$12.80	$12.80
Purchase #2	$250.81	4.306%	$261.6099	$261.61	$261.60	$261.60
Purchase #3	$211.66	5.548%	$223.4029	$223.40	$223.40	$223.40
Purchase #4	$134.32	7.270%	$144.0851	$144.09	$144.10	$144.10
Purchase #5	$117.84	8.564%	$127.9318	$127.93	$127.95	$127.90
Purchase #6	$190.65	5.198%	$200.56	$200.56	$200.55	$200.60
Purchase #7	$29.27	11.456%	$32.6232	$32.62	$32.60	$32.60
7 purchase totals =	$946.03		$1,002.9946	$1,002.99	$1,003.00	$1,003.00