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	$227.90	12.457%	$256.2895	$256.29	$256.30	$256.30
Purchase #2	$22.84	9.812%	$25.0811	$25.08	$25.10	$25.10
Purchase #3	$46.29	12.186%	$51.9309	$51.93	$51.95	$51.90
Purchase #4	$53.57	10.420%	$59.152	$59.15	$59.15	$59.20
Purchase #5	$45.40	13.186%	$51.3864	$51.39	$51.40	$51.40
Purchase #6	$37.55	13.393%	$42.5791	$42.58	$42.60	$42.60
Purchase #7	$74.45	6.581%	$79.3496	$79.35	$79.35	$79.30
7 purchase totals =	$508.00		$565.7686	$565.77	$565.85	$565.80