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	$191.78	9.744%	$210.467	$210.47	$210.45	$210.50
Purchase #2	$115.32	5.431%	$121.583	$121.58	$121.60	$121.60
Purchase #3	$196.38	11.386%	$218.7398	$218.74	$218.75	$218.70
Purchase #4	$85.49	5.596%	$90.274	$90.27	$90.25	$90.30
Purchase #5	$64.44	3.705%	$66.8275	$66.83	$66.85	$66.80
Purchase #6	$185.95	13.667%	$211.3638	$211.36	$211.35	$211.40
Purchase #7	$29.40	10.661%	$32.5343	$32.53	$32.55	$32.50
7 purchase totals =	$868.76		$951.7894	$951.78	$951.80	$951.80