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	$13.87	10.318%	$15.3011	$15.30	$15.30	$15.30
Purchase #2	$107.70	5.159%	$113.2562	$113.26	$113.25	$113.30
Purchase #3	$97.66	5.707%	$103.2335	$103.23	$103.25	$103.20
Purchase #4	$86.82	4.591%	$90.8059	$90.81	$90.80	$90.80
Purchase #5	$35.56	4.789%	$37.263	$37.26	$37.25	$37.30
Purchase #6	$60.48	10.192%	$66.6441	$66.64	$66.65	$66.60
Purchase #7	$134.94	12.434%	$151.7184	$151.72	$151.70	$151.70
7 purchase totals =	$537.03		$578.2222	$578.22	$578.20	$578.20