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	$129.38	6.565%	$137.8738	$137.87	$137.85	$137.90
Purchase #2	$16.65	5.153%	$17.508	$17.51	$17.50	$17.50
Purchase #3	$240.87	8.152%	$260.5057	$260.51	$260.50	$260.50
Purchase #4	$93.54	7.149%	$100.2272	$100.23	$100.25	$100.20
Purchase #5	$129.48	10.333%	$142.8592	$142.86	$142.85	$142.90
Purchase #6	$225.31	6.213%	$239.3085	$239.31	$239.30	$239.30
Purchase #7	$94.58	9.217%	$103.2974	$103.30	$103.30	$103.30
7 purchase totals =	$929.81		$1,001.5798	$1,001.59	$1,001.55	$1,001.60