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	$59.59	12.187%	$66.8522	$66.85	$66.85	$66.90
Purchase #2	$115.26	7.691%	$124.1246	$124.12	$124.10	$124.10
Purchase #3	$113.80	12.151%	$127.6278	$127.63	$127.65	$127.60
Purchase #4	$68.91	5.153%	$72.4609	$72.46	$72.45	$72.50
Purchase #5	$242.75	7.161%	$260.1333	$260.13	$260.15	$260.10
Purchase #6	$118.94	3.518%	$123.1243	$123.12	$123.10	$123.10
Purchase #7	$5.95	11.169%	$6.6146	$6.61	$6.60	$6.60
7 purchase totals =	$725.20		$780.9377	$780.92	$780.90	$780.90