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	$200.83	6.291%	$213.4642	$213.46	$213.45	$213.50
Purchase #2	$158.28	9.574%	$173.4337	$173.43	$173.45	$173.40
Purchase #3	$235.88	8.544%	$256.0336	$256.03	$256.05	$256.00
Purchase #4	$7.29	6.750%	$7.7821	$7.78	$7.80	$7.80
Purchase #5	$130.96	5.291%	$137.8891	$137.89	$137.90	$137.90
Purchase #6	$214.79	4.209%	$223.8305	$223.83	$223.85	$223.80
Purchase #7	$189.56	7.575%	$203.9192	$203.92	$203.90	$203.90
7 purchase totals =	$1,137.59		$1,216.3524	$1,216.34	$1,216.40	$1,216.30