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	$138.65	5.863%	$146.779	$146.78	$146.80	$146.80
Purchase #2	$141.36	7.787%	$152.3677	$152.37	$152.35	$152.40
Purchase #3	$158.70	13.808%	$180.6133	$180.61	$180.60	$180.60
Purchase #4	$168.44	11.314%	$187.4973	$187.50	$187.50	$187.50
Purchase #5	$113.63	13.478%	$128.9451	$128.95	$128.95	$128.90
Purchase #6	$53.94	10.546%	$59.6285	$59.63	$59.65	$59.60
Purchase #7	$92.98	10.814%	$103.0349	$103.03	$103.05	$103.00
7 purchase totals =	$867.70		$958.8658	$958.87	$958.90	$958.80