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	$5.78	12.527%	$6.5041	$6.50	$6.50	$6.50
Purchase #2	$112.70	9.158%	$123.0211	$123.02	$123.00	$123.00
Purchase #3	$148.72	3.233%	$153.5281	$153.53	$153.55	$153.50
Purchase #4	$82.76	9.195%	$90.3698	$90.37	$90.35	$90.40
Purchase #5	$117.33	7.555%	$126.1943	$126.19	$126.20	$126.20
Purchase #6	$173.77	9.559%	$190.3807	$190.38	$190.40	$190.40
Purchase #7	$223.79	3.578%	$231.7972	$231.80	$231.80	$231.80
7 purchase totals =	$864.85		$921.7953	$921.79	$921.80	$921.80