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	$228.82	3.504%	$236.8379	$236.84	$236.85	$236.80
Purchase #2	$135.88	9.229%	$148.4204	$148.42	$148.40	$148.40
Purchase #3	$226.61	12.836%	$255.6977	$255.70	$255.70	$255.70
Purchase #4	$114.68	7.823%	$123.6514	$123.65	$123.65	$123.70
Purchase #5	$47.50	9.451%	$51.9892	$51.99	$52.00	$52.00
Purchase #6	$47.52	12.823%	$53.6135	$53.61	$53.60	$53.60
Purchase #7	$79.82	13.586%	$90.6643	$90.66	$90.65	$90.70
7 purchase totals =	$880.83		$960.8744	$960.87	$960.85	$960.90