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	$93.96	5.453%	$99.0836	$99.08	$99.10	$99.10
Purchase #2	$202.78	7.291%	$217.5647	$217.56	$217.55	$217.60
Purchase #3	$98.69	13.406%	$111.9204	$111.92	$111.90	$111.90
Purchase #4	$14.89	13.236%	$16.8608	$16.86	$16.85	$16.90
Purchase #5	$34.95	13.530%	$39.6787	$39.68	$39.70	$39.70
Purchase #6	$127.69	12.723%	$143.936	$143.94	$143.95	$143.90
Purchase #7	$5.32	4.694%	$5.5697	$5.57	$5.55	$5.60
7 purchase totals =	$578.28		$634.6139	$634.61	$634.60	$634.70