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	$144.94	13.663%	$164.7432	$164.74	$164.75	$164.70
Purchase #2	$40.38	5.175%	$42.4697	$42.47	$42.45	$42.50
Purchase #3	$141.84	8.285%	$153.5914	$153.59	$153.60	$153.60
Purchase #4	$152.97	7.108%	$163.8431	$163.84	$163.85	$163.80
Purchase #5	$63.67	10.739%	$70.5075	$70.51	$70.50	$70.50
Purchase #6	$83.51	8.544%	$90.6451	$90.65	$90.65	$90.60
Purchase #7	$64.78	3.546%	$67.0771	$67.08	$67.10	$67.10
7 purchase totals =	$692.09		$752.8771	$752.88	$752.90	$752.80