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	$25.30	13.184%	$28.6356	$28.64	$28.65	$28.60
Purchase #2	$77.37	6.791%	$82.6242	$82.62	$82.60	$82.60
Purchase #3	$201.35	10.554%	$222.6005	$222.60	$222.60	$222.60
Purchase #4	$70.82	5.372%	$74.6245	$74.62	$74.60	$74.60
Purchase #5	$164.72	5.572%	$173.8982	$173.90	$173.90	$173.90
Purchase #6	$218.81	5.248%	$230.2931	$230.29	$230.30	$230.30
Purchase #7	$240.31	7.804%	$259.0638	$259.06	$259.05	$259.10
7 purchase totals =	$998.68		$1,071.7399	$1,071.73	$1,071.70	$1,071.70