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	$246.78	13.729%	$280.6604	$280.66	$280.65	$280.70
Purchase #2	$77.72	11.394%	$86.5754	$86.58	$86.60	$86.60
Purchase #3	$98.70	5.579%	$104.2065	$104.21	$104.20	$104.20
Purchase #4	$10.82	11.607%	$12.0759	$12.08	$12.10	$12.10
Purchase #5	$55.91	8.344%	$60.5751	$60.58	$60.60	$60.60
Purchase #6	$158.94	8.572%	$172.5643	$172.56	$172.55	$172.60
Purchase #7	$101.89	3.695%	$105.6548	$105.65	$105.65	$105.70
7 purchase totals =	$750.76		$822.3124	$822.32	$822.35	$822.50