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	$75.79	5.823%	$80.2033	$80.20	$80.20	$80.20
Purchase #2	$108.49	7.145%	$116.2416	$116.24	$116.25	$116.20
Purchase #3	$246.78	13.650%	$280.4655	$280.47	$280.45	$280.50
Purchase #4	$173.68	10.861%	$192.5434	$192.54	$192.55	$192.50
Purchase #5	$82.52	7.152%	$88.4218	$88.42	$88.40	$88.40
Purchase #6	$240.52	5.441%	$253.6067	$253.61	$253.60	$253.60
Purchase #7	$125.33	10.839%	$138.9145	$138.91	$138.90	$138.90
7 purchase totals =	$1,053.11		$1,150.3968	$1,150.39	$1,150.35	$1,150.30