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	$37.99	13.699%	$43.1943	$43.19	$43.20	$43.20
Purchase #2	$132.66	3.446%	$137.2315	$137.23	$137.25	$137.20
Purchase #3	$193.84	3.164%	$199.9731	$199.97	$199.95	$200.00
Purchase #4	$245.32	10.844%	$271.9225	$271.92	$271.90	$271.90
Purchase #5	$43.27	4.523%	$45.2271	$45.23	$45.25	$45.20
Purchase #6	$123.32	4.291%	$128.6117	$128.61	$128.60	$128.60
Purchase #7	$135.27	7.667%	$145.6412	$145.64	$145.65	$145.60
7 purchase totals =	$911.67		$971.8014	$971.79	$971.80	$971.70