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	$231.62	8.138%	$250.4692	$250.47	$250.45	$250.50
Purchase #2	$5.92	8.480%	$6.422	$6.42	$6.40	$6.40
Purchase #3	$32.99	13.710%	$37.5129	$37.51	$37.50	$37.50
Purchase #4	$30.50	8.111%	$32.9739	$32.97	$32.95	$33.00
Purchase #5	$36.56	6.581%	$38.966	$38.97	$38.95	$39.00
Purchase #6	$100.33	11.247%	$111.6141	$111.61	$111.60	$111.60
Purchase #7	$130.28	7.532%	$140.0927	$140.09	$140.10	$140.10
7 purchase totals =	$568.20		$618.0508	$618.04	$617.95	$618.10