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	$8.60	11.421%	$9.5822	$9.58	$9.60	$9.60
Purchase #2	$163.30	7.217%	$175.0854	$175.09	$175.10	$175.10
Purchase #3	$155.59	5.774%	$164.5738	$164.57	$164.55	$164.60
Purchase #4	$106.59	11.873%	$119.2454	$119.25	$119.25	$119.20
Purchase #5	$18.33	9.162%	$20.0094	$20.01	$20.00	$20.00
Purchase #6	$179.65	9.584%	$196.8677	$196.87	$196.85	$196.90
Purchase #7	$151.58	4.557%	$158.4875	$158.49	$158.50	$158.50
7 purchase totals =	$783.64		$843.8514	$843.86	$843.85	$843.90