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	$249.46	12.421%	$280.4454	$280.45	$280.45	$280.40
Purchase #2	$173.89	13.275%	$196.9739	$196.97	$196.95	$197.00
Purchase #3	$167.32	3.522%	$173.213	$173.21	$173.20	$173.20
Purchase #4	$31.97	8.154%	$34.5768	$34.58	$34.60	$34.60
Purchase #5	$231.34	13.868%	$263.4222	$263.42	$263.40	$263.40
Purchase #6	$16.53	8.117%	$17.8717	$17.87	$17.85	$17.90
Purchase #7	$107.56	3.774%	$111.6193	$111.62	$111.60	$111.60
7 purchase totals =	$978.07		$1,078.1223	$1,078.12	$1,078.05	$1,078.10