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	$132.89	10.218%	$146.4687	$146.47	$146.45	$146.50
Purchase #2	$235.52	7.837%	$253.9777	$253.98	$254.00	$254.00
Purchase #3	$148.92	5.446%	$157.0302	$157.03	$157.05	$157.00
Purchase #4	$194.50	10.233%	$214.4032	$214.40	$214.40	$214.40
Purchase #5	$38.39	10.347%	$42.3622	$42.36	$42.35	$42.40
Purchase #6	$126.64	8.645%	$137.588	$137.59	$137.60	$137.60
Purchase #7	$40.45	4.747%	$42.3702	$42.37	$42.35	$42.40
7 purchase totals =	$917.31		$994.2002	$994.20	$994.20	$994.30