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	$77.45	4.335%	$80.8075	$80.81	$80.80	$80.80
Purchase #2	$191.46	4.533%	$200.1389	$200.14	$200.15	$200.10
Purchase #3	$27.29	6.699%	$29.1182	$29.12	$29.10	$29.10
Purchase #4	$25.50	8.700%	$27.7185	$27.72	$27.70	$27.70
Purchase #5	$10.55	12.418%	$11.8601	$11.86	$11.85	$11.90
Purchase #6	$204.83	9.104%	$223.4777	$223.48	$223.50	$223.50
Purchase #7	$85.81	3.853%	$89.1163	$89.12	$89.10	$89.10
7 purchase totals =	$622.89		$662.2372	$662.25	$662.20	$662.20