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	$122.77	12.249%	$137.8081	$137.81	$137.80	$137.80
Purchase #2	$87.27	3.801%	$90.5871	$90.59	$90.60	$90.60
Purchase #3	$103.34	13.763%	$117.5627	$117.56	$117.55	$117.60
Purchase #4	$162.68	3.331%	$168.0989	$168.10	$168.10	$168.10
Purchase #5	$223.28	10.853%	$247.5126	$247.51	$247.50	$247.50
Purchase #6	$95.86	9.557%	$105.0213	$105.02	$105.00	$105.00
Purchase #7	$190.91	13.281%	$216.2648	$216.26	$216.25	$216.30
7 purchase totals =	$986.11		$1,082.8555	$1,082.85	$1,082.80	$1,082.90