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	$136.55	5.630%	$144.2378	$144.24	$144.25	$144.20
Purchase #2	$34.90	11.704%	$38.9847	$38.98	$39.00	$39.00
Purchase #3	$248.50	5.139%	$261.2704	$261.27	$261.25	$261.30
Purchase #4	$137.94	11.340%	$153.5824	$153.58	$153.60	$153.60
Purchase #5	$105.93	8.504%	$114.9383	$114.94	$114.95	$114.90
Purchase #6	$210.51	10.697%	$233.0283	$233.03	$233.05	$233.00
Purchase #7	$122.43	9.835%	$134.471	$134.47	$134.45	$134.50
7 purchase totals =	$996.76		$1,080.5129	$1,080.51	$1,080.55	$1,080.50