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	$113.36	8.832%	$123.372	$123.37	$123.35	$123.40
Purchase #2	$27.46	7.285%	$29.4605	$29.46	$29.45	$29.50
Purchase #3	$196.52	5.815%	$207.9476	$207.95	$207.95	$207.90
Purchase #4	$94.49	10.561%	$104.4691	$104.47	$104.45	$104.50
Purchase #5	$47.75	13.429%	$54.1623	$54.16	$54.15	$54.20
Purchase #6	$117.53	10.168%	$129.4805	$129.48	$129.50	$129.50
Purchase #7	$33.59	12.105%	$37.6561	$37.66	$37.65	$37.70
7 purchase totals =	$630.70		$686.5481	$686.55	$686.50	$686.70