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	$229.67	11.445%	$255.9557	$255.96	$255.95	$256.00
Purchase #2	$228.42	11.492%	$254.67	$254.67	$254.65	$254.70
Purchase #3	$104.72	3.760%	$108.6575	$108.66	$108.65	$108.70
Purchase #4	$55.51	3.626%	$57.5228	$57.52	$57.50	$57.50
Purchase #5	$71.47	12.466%	$80.3795	$80.38	$80.40	$80.40
Purchase #6	$185.56	10.655%	$205.3314	$205.33	$205.35	$205.30
Purchase #7	$158.43	13.697%	$180.1302	$180.13	$180.15	$180.10
7 purchase totals =	$1,033.78		$1,142.6471	$1,142.65	$1,142.65	$1,142.70