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	$9.89	5.798%	$10.4634	$10.46	$10.45	$10.50
Purchase #2	$61.77	5.849%	$65.3829	$65.38	$65.40	$65.40
Purchase #3	$173.97	13.233%	$196.9915	$196.99	$197.00	$197.00
Purchase #4	$189.81	13.493%	$215.4211	$215.42	$215.40	$215.40
Purchase #5	$93.71	10.850%	$103.8775	$103.88	$103.90	$103.90
Purchase #6	$70.83	9.363%	$77.4618	$77.46	$77.45	$77.50
Purchase #7	$134.54	10.526%	$148.7017	$148.70	$148.70	$148.70
7 purchase totals =	$734.52		$818.2999	$818.29	$818.30	$818.40