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	$139.77	7.681%	$150.5057	$150.51	$150.50	$150.50
Purchase #2	$144.68	5.518%	$152.6634	$152.66	$152.65	$152.70
Purchase #3	$244.95	4.858%	$256.8497	$256.85	$256.85	$256.80
Purchase #4	$79.57	10.477%	$87.9065	$87.91	$87.90	$87.90
Purchase #5	$12.32	3.155%	$12.7087	$12.71	$12.70	$12.70
Purchase #6	$116.97	5.524%	$123.4314	$123.43	$123.45	$123.40
Purchase #7	$194.77	10.688%	$215.587	$215.59	$215.60	$215.60
7 purchase totals =	$933.03		$999.6524	$999.66	$999.65	$999.60