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	$244.59	11.348%	$272.3461	$272.35	$272.35	$272.30
Purchase #2	$90.43	11.163%	$100.5247	$100.52	$100.50	$100.50
Purchase #3	$238.71	7.828%	$257.3962	$257.40	$257.40	$257.40
Purchase #4	$114.90	5.649%	$121.3907	$121.39	$121.40	$121.40
Purchase #5	$219.33	10.771%	$242.954	$242.95	$242.95	$243.00
Purchase #6	$108.31	4.443%	$113.1222	$113.12	$113.10	$113.10
Purchase #7	$155.35	11.284%	$172.8797	$172.88	$172.90	$172.90
7 purchase totals =	$1,171.62		$1,280.6136	$1,280.61	$1,280.60	$1,280.60