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	$98.62	3.462%	$102.0342	$102.03	$102.05	$102.00
Purchase #2	$110.92	7.754%	$119.5207	$119.52	$119.50	$119.50
Purchase #3	$44.73	6.705%	$47.7291	$47.73	$47.75	$47.70
Purchase #4	$163.90	5.866%	$173.5144	$173.51	$173.50	$173.50
Purchase #5	$6.90	11.459%	$7.6907	$7.69	$7.70	$7.70
Purchase #6	$12.89	5.695%	$13.6241	$13.62	$13.60	$13.60
Purchase #7	$115.95	9.663%	$127.1542	$127.15	$127.15	$127.20
7 purchase totals =	$553.91		$591.2674	$591.25	$591.25	$591.20