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	$176.81	6.561%	$188.4105	$188.41	$188.40	$188.40
Purchase #2	$90.55	13.294%	$102.5877	$102.59	$102.60	$102.60
Purchase #3	$126.86	5.708%	$134.1012	$134.10	$134.10	$134.10
Purchase #4	$156.33	9.791%	$171.6363	$171.64	$171.65	$171.60
Purchase #5	$244.50	3.720%	$253.5954	$253.60	$253.60	$253.60
Purchase #6	$237.94	7.485%	$255.7498	$255.75	$255.75	$255.70
Purchase #7	$222.83	4.650%	$233.1916	$233.19	$233.20	$233.20
7 purchase totals =	$1,255.82		$1,339.2725	$1,339.28	$1,339.30	$1,339.20