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	$226.51	12.824%	$255.5576	$255.56	$255.55	$255.60
Purchase #2	$145.29	3.513%	$150.394	$150.39	$150.40	$150.40
Purchase #3	$142.87	3.669%	$148.1119	$148.11	$148.10	$148.10
Purchase #4	$71.42	12.178%	$80.1175	$80.12	$80.10	$80.10
Purchase #5	$114.45	12.240%	$128.4587	$128.46	$128.45	$128.50
Purchase #6	$184.65	11.367%	$205.6392	$205.64	$205.65	$205.60
Purchase #7	$21.85	6.539%	$23.2788	$23.28	$23.30	$23.30
7 purchase totals =	$907.04		$991.5577	$991.56	$991.55	$991.60