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	$246.86	13.757%	$280.8205	$280.82	$280.80	$280.80
Purchase #2	$54.70	5.321%	$57.6106	$57.61	$57.60	$57.60
Purchase #3	$216.68	6.365%	$230.4717	$230.47	$230.45	$230.50
Purchase #4	$81.95	13.410%	$92.9395	$92.94	$92.95	$92.90
Purchase #5	$34.73	10.427%	$38.3513	$38.35	$38.35	$38.40
Purchase #6	$50.91	8.248%	$55.1091	$55.11	$55.10	$55.10
Purchase #7	$129.71	12.172%	$145.4983	$145.50	$145.50	$145.50
7 purchase totals =	$815.54		$900.8010	$900.80	$900.75	$900.80