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	$250.88	10.551%	$277.3503	$277.35	$277.35	$277.40
Purchase #2	$22.55	6.137%	$23.9339	$23.93	$23.95	$23.90
Purchase #3	$185.91	5.855%	$196.795	$196.80	$196.80	$196.80
Purchase #4	$83.49	3.748%	$86.6192	$86.62	$86.60	$86.60
Purchase #5	$97.80	5.835%	$103.5066	$103.51	$103.50	$103.50
Purchase #6	$123.50	3.176%	$127.4224	$127.42	$127.40	$127.40
Purchase #7	$107.65	10.716%	$119.1858	$119.19	$119.20	$119.20
7 purchase totals =	$871.78		$934.8132	$934.82	$934.80	$934.80