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	$21.26	8.294%	$23.0233	$23.02	$23.00	$23.00
Purchase #2	$99.49	13.634%	$113.0545	$113.05	$113.05	$113.10
Purchase #3	$164.96	5.182%	$173.5082	$173.51	$173.50	$173.50
Purchase #4	$215.50	3.472%	$222.9822	$222.98	$223.00	$223.00
Purchase #5	$158.52	12.672%	$178.6077	$178.61	$178.60	$178.60
Purchase #6	$131.72	12.725%	$148.4814	$148.48	$148.50	$148.50
Purchase #7	$59.67	9.794%	$65.5141	$65.51	$65.50	$65.50
7 purchase totals =	$851.12		$925.1714	$925.16	$925.15	$925.20