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	$242.62	10.595%	$268.3256	$268.33	$268.35	$268.30
Purchase #2	$46.78	3.737%	$48.5282	$48.53	$48.55	$48.50
Purchase #3	$153.40	12.641%	$172.7913	$172.79	$172.80	$172.80
Purchase #4	$26.27	6.491%	$27.9752	$27.98	$28.00	$28.00
Purchase #5	$70.48	10.545%	$77.9121	$77.91	$77.90	$77.90
Purchase #6	$38.60	9.841%	$42.3986	$42.40	$42.40	$42.40
Purchase #7	$71.32	10.566%	$78.8557	$78.86	$78.85	$78.90
7 purchase totals =	$649.47		$716.7867	$716.80	$716.85	$716.80