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	$250.67	11.591%	$279.7252	$279.73	$279.75	$279.70
Purchase #2	$64.30	13.475%	$72.9644	$72.96	$72.95	$73.00
Purchase #3	$159.58	10.586%	$176.4731	$176.47	$176.45	$176.50
Purchase #4	$37.55	6.631%	$40.0399	$40.04	$40.05	$40.00
Purchase #5	$217.77	4.500%	$227.5697	$227.57	$227.55	$227.60
Purchase #6	$44.74	8.379%	$48.4888	$48.49	$48.50	$48.50
Purchase #7	$45.93	12.294%	$51.5766	$51.58	$51.60	$51.60
7 purchase totals =	$820.54		$896.8377	$896.84	$896.85	$896.90