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	$55.69	6.271%	$59.1823	$59.18	$59.20	$59.20
Purchase #2	$15.68	11.462%	$17.4772	$17.48	$17.50	$17.50
Purchase #3	$74.30	12.687%	$83.7264	$83.73	$83.75	$83.70
Purchase #4	$60.92	9.252%	$66.5563	$66.56	$66.55	$66.60
Purchase #5	$17.45	9.122%	$19.0418	$19.04	$19.05	$19.00
Purchase #6	$198.93	12.547%	$223.8897	$223.89	$223.90	$223.90
Purchase #7	$221.53	12.841%	$249.9767	$249.98	$250.00	$250.00
7 purchase totals =	$644.50		$719.8504	$719.86	$719.95	$719.90