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	$162.39	13.183%	$183.7979	$183.80	$183.80	$183.80
Purchase #2	$241.91	6.181%	$256.8625	$256.86	$256.85	$256.90
Purchase #3	$237.48	10.106%	$261.4797	$261.48	$261.50	$261.50
Purchase #4	$35.65	4.727%	$37.3352	$37.34	$37.35	$37.30
Purchase #5	$80.27	10.192%	$88.4511	$88.45	$88.45	$88.50
Purchase #6	$104.98	12.245%	$117.8348	$117.83	$117.85	$117.80
Purchase #7	$32.45	12.506%	$36.5082	$36.51	$36.50	$36.50
7 purchase totals =	$895.13		$982.2694	$982.27	$982.30	$982.30