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	$15.65	8.632%	$17.0009	$17.00	$17.00	$17.00
Purchase #2	$128.48	12.788%	$144.91	$144.91	$144.90	$144.90
Purchase #3	$189.29	5.207%	$199.1463	$199.15	$199.15	$199.10
Purchase #4	$60.38	9.144%	$65.9011	$65.90	$65.90	$65.90
Purchase #5	$104.68	13.244%	$118.5438	$118.54	$118.55	$118.50
Purchase #6	$237.91	13.853%	$270.8677	$270.87	$270.85	$270.90
Purchase #7	$93.99	6.710%	$100.2967	$100.30	$100.30	$100.30
7 purchase totals =	$830.38		$916.6665	$916.67	$916.65	$916.60