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	$216.93	7.478%	$233.152	$233.15	$233.15	$233.20
Purchase #2	$90.37	9.384%	$98.8503	$98.85	$98.85	$98.90
Purchase #3	$212.27	8.455%	$230.2174	$230.22	$230.20	$230.20
Purchase #4	$165.98	4.113%	$172.8068	$172.81	$172.80	$172.80
Purchase #5	$249.31	6.650%	$265.8891	$265.89	$265.90	$265.90
Purchase #6	$124.37	10.762%	$137.7547	$137.75	$137.75	$137.80
Purchase #7	$62.58	12.443%	$70.3668	$70.37	$70.35	$70.40
7 purchase totals =	$1,121.81		$1,209.0371	$1,209.04	$1,209.00	$1,209.20