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	$13.64	6.340%	$14.5048	$14.50	$14.50	$14.50
Purchase #2	$93.95	12.394%	$105.5942	$105.59	$105.60	$105.60
Purchase #3	$217.44	4.786%	$227.8467	$227.85	$227.85	$227.80
Purchase #4	$148.51	12.263%	$166.7218	$166.72	$166.70	$166.70
Purchase #5	$113.45	8.779%	$123.4098	$123.41	$123.40	$123.40
Purchase #6	$33.87	10.106%	$37.2929	$37.29	$37.30	$37.30
Purchase #7	$161.55	12.235%	$181.3156	$181.32	$181.30	$181.30
7 purchase totals =	$782.41		$856.6858	$856.68	$856.65	$856.60