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	$34.61	11.779%	$38.6867	$38.69	$38.70	$38.70
Purchase #2	$214.28	3.730%	$222.2726	$222.27	$222.25	$222.30
Purchase #3	$204.87	8.210%	$221.6898	$221.69	$221.70	$221.70
Purchase #4	$138.35	3.345%	$142.9778	$142.98	$143.00	$143.00
Purchase #5	$146.58	12.456%	$164.838	$164.84	$164.85	$164.80
Purchase #6	$145.90	9.730%	$160.0961	$160.10	$160.10	$160.10
Purchase #7	$213.43	4.295%	$222.5968	$222.60	$222.60	$222.60
7 purchase totals =	$1,098.02		$1,173.1578	$1,173.17	$1,173.20	$1,173.20