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	$100.36	5.144%	$105.5225	$105.52	$105.50	$105.50
Purchase #2	$46.39	10.340%	$51.1867	$51.19	$51.20	$51.20
Purchase #3	$131.72	11.487%	$146.8507	$146.85	$146.85	$146.90
Purchase #4	$224.38	8.363%	$243.1449	$243.14	$243.15	$243.10
Purchase #5	$74.27	12.340%	$83.4349	$83.43	$83.45	$83.40
Purchase #6	$70.35	10.675%	$77.8599	$77.86	$77.85	$77.90
Purchase #7	$166.65	12.693%	$187.8029	$187.80	$187.80	$187.80
7 purchase totals =	$814.12		$895.8025	$895.79	$895.80	$895.80