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	$162.51	11.256%	$180.8021	$180.80	$180.80	$180.80
Purchase #2	$172.29	10.764%	$190.8353	$190.84	$190.85	$190.80
Purchase #3	$207.81	11.354%	$231.4047	$231.40	$231.40	$231.40
Purchase #4	$139.58	13.694%	$158.6941	$158.69	$158.70	$158.70
Purchase #5	$113.30	9.702%	$124.2924	$124.29	$124.30	$124.30
Purchase #6	$183.67	13.716%	$208.8622	$208.86	$208.85	$208.90
Purchase #7	$112.95	13.738%	$128.4671	$128.47	$128.45	$128.50
7 purchase totals =	$1,092.11		$1,223.3579	$1,223.35	$1,223.35	$1,223.40