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	$37.30	13.545%	$42.3523	$42.35	$42.35	$42.40
Purchase #2	$41.97	11.168%	$46.6572	$46.66	$46.65	$46.70
Purchase #3	$132.25	5.546%	$139.5846	$139.58	$139.60	$139.60
Purchase #4	$55.88	11.697%	$62.4163	$62.42	$62.40	$62.40
Purchase #5	$219.71	8.626%	$238.6622	$238.66	$238.65	$238.70
Purchase #6	$42.32	5.286%	$44.557	$44.56	$44.55	$44.60
Purchase #7	$189.64	8.575%	$205.9016	$205.90	$205.90	$205.90
7 purchase totals =	$719.07		$780.1312	$780.13	$780.10	$780.30