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	$166.37	7.382%	$178.6514	$178.65	$178.65	$178.70
Purchase #2	$142.39	4.503%	$148.8018	$148.80	$148.80	$148.80
Purchase #3	$83.72	10.396%	$92.4235	$92.42	$92.40	$92.40
Purchase #4	$162.39	13.732%	$184.6894	$184.69	$184.70	$184.70
Purchase #5	$241.93	6.858%	$258.5216	$258.52	$258.50	$258.50
Purchase #6	$123.95	13.818%	$141.0774	$141.08	$141.10	$141.10
Purchase #7	$109.42	12.585%	$123.1905	$123.19	$123.20	$123.20
7 purchase totals =	$1,030.17		$1,127.3556	$1,127.35	$1,127.35	$1,127.40