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	$154.29	10.522%	$170.5244	$170.52	$170.50	$170.50
Purchase #2	$164.35	7.531%	$176.7272	$176.73	$176.75	$176.70
Purchase #3	$70.88	9.735%	$77.7802	$77.78	$77.80	$77.80
Purchase #4	$63.69	12.703%	$71.7805	$71.78	$71.80	$71.80
Purchase #5	$200.49	12.687%	$225.9262	$225.93	$225.95	$225.90
Purchase #6	$136.72	5.114%	$143.7119	$143.71	$143.70	$143.70
Purchase #7	$28.72	13.452%	$32.5834	$32.58	$32.60	$32.60
7 purchase totals =	$819.14		$899.0338	$899.03	$899.10	$899.00