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	$161.35	11.562%	$180.0053	$180.01	$180.00	$180.00
Purchase #2	$244.39	3.430%	$252.7726	$252.77	$252.75	$252.80
Purchase #3	$161.53	11.586%	$180.2449	$180.24	$180.25	$180.20
Purchase #4	$95.86	5.207%	$100.8514	$100.85	$100.85	$100.90
Purchase #5	$37.65	6.286%	$40.0167	$40.02	$40.00	$40.00
Purchase #6	$66.29	6.524%	$70.6148	$70.61	$70.60	$70.60
Purchase #7	$108.50	13.792%	$123.4643	$123.46	$123.45	$123.50
7 purchase totals =	$875.57		$947.9700	$947.96	$947.90	$948.00