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	$76.45	5.239%	$80.4552	$80.46	$80.45	$80.50
Purchase #2	$93.27	4.183%	$97.1715	$97.17	$97.15	$97.20
Purchase #3	$228.65	10.721%	$253.1636	$253.16	$253.15	$253.20
Purchase #4	$215.37	7.355%	$231.2105	$231.21	$231.20	$231.20
Purchase #5	$165.41	10.240%	$182.348	$182.35	$182.35	$182.30
Purchase #6	$127.90	12.283%	$143.61	$143.61	$143.60	$143.60
Purchase #7	$140.90	5.456%	$148.5875	$148.59	$148.60	$148.60
7 purchase totals =	$1,047.95		$1,136.5463	$1,136.55	$1,136.50	$1,136.60