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	$15.56	10.730%	$17.2296	$17.23	$17.25	$17.20
Purchase #2	$171.44	7.680%	$184.6066	$184.61	$184.60	$184.60
Purchase #3	$113.47	12.339%	$127.4711	$127.47	$127.45	$127.50
Purchase #4	$78.64	11.722%	$87.8582	$87.86	$87.85	$87.90
Purchase #5	$77.32	11.863%	$86.4925	$86.49	$86.50	$86.50
Purchase #6	$98.57	4.210%	$102.7198	$102.72	$102.70	$102.70
Purchase #7	$158.92	4.621%	$166.2637	$166.26	$166.25	$166.30
7 purchase totals =	$713.92		$772.6415	$772.64	$772.60	$772.70