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	$156.77	10.729%	$173.5899	$173.59	$173.60	$173.60
Purchase #2	$113.67	12.216%	$127.5559	$127.56	$127.55	$127.60
Purchase #3	$80.45	4.105%	$83.7525	$83.75	$83.75	$83.80
Purchase #4	$176.92	13.297%	$200.4451	$200.45	$200.45	$200.40
Purchase #5	$108.42	9.706%	$118.9432	$118.94	$118.95	$118.90
Purchase #6	$34.52	12.353%	$38.7843	$38.78	$38.80	$38.80
Purchase #7	$76.85	8.824%	$83.6312	$83.63	$83.65	$83.60
7 purchase totals =	$747.60		$826.7021	$826.70	$826.75	$826.70