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	$7.60	3.451%	$7.8623	$7.86	$7.85	$7.90
Purchase #2	$191.97	5.716%	$202.943	$202.94	$202.95	$202.90
Purchase #3	$62.87	4.368%	$65.6162	$65.62	$65.60	$65.60
Purchase #4	$79.77	13.138%	$90.2502	$90.25	$90.25	$90.30
Purchase #5	$13.60	4.156%	$14.1652	$14.17	$14.15	$14.20
Purchase #6	$32.57	4.475%	$34.0275	$34.03	$34.05	$34.00
Purchase #7	$89.50	12.690%	$100.8576	$100.86	$100.85	$100.90
7 purchase totals =	$477.88		$515.7220	$515.73	$515.70	$515.80