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	$50.37	12.262%	$56.5464	$56.55	$56.55	$56.50
Purchase #2	$94.73	11.603%	$105.7215	$105.72	$105.70	$105.70
Purchase #3	$42.54	6.178%	$45.1681	$45.17	$45.15	$45.20
Purchase #4	$123.85	7.125%	$132.6743	$132.67	$132.65	$132.70
Purchase #5	$171.29	7.556%	$184.2327	$184.23	$184.25	$184.20
Purchase #6	$206.70	11.584%	$230.6441	$230.64	$230.65	$230.60
Purchase #7	$103.28	9.246%	$112.8293	$112.83	$112.85	$112.80
7 purchase totals =	$792.76		$867.8164	$867.81	$867.80	$867.70