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	$113.51	13.475%	$128.8055	$128.81	$128.80	$128.80
Purchase #2	$100.29	4.861%	$105.1651	$105.17	$105.15	$105.20
Purchase #3	$158.87	7.291%	$170.4532	$170.45	$170.45	$170.50
Purchase #4	$171.75	11.559%	$191.6026	$191.60	$191.60	$191.60
Purchase #5	$48.96	5.762%	$51.7811	$51.78	$51.80	$51.80
Purchase #6	$35.78	3.504%	$37.0337	$37.03	$37.05	$37.00
Purchase #7	$172.62	7.692%	$185.8979	$185.90	$185.90	$185.90
7 purchase totals =	$801.78		$870.7391	$870.74	$870.75	$870.80