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	$91.69	9.232%	$100.1548	$100.15	$100.15	$100.20
Purchase #2	$67.89	12.637%	$76.4693	$76.47	$76.45	$76.50
Purchase #3	$100.29	4.671%	$104.9745	$104.97	$104.95	$105.00
Purchase #4	$192.32	3.353%	$198.7685	$198.77	$198.75	$198.80
Purchase #5	$205.81	5.343%	$216.8064	$216.81	$216.80	$216.80
Purchase #6	$38.70	9.262%	$42.2844	$42.28	$42.30	$42.30
Purchase #7	$123.31	3.720%	$127.8971	$127.90	$127.90	$127.90
7 purchase totals =	$820.01		$867.3550	$867.35	$867.30	$867.50