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	$63.44	8.528%	$68.8502	$68.85	$68.85	$68.90
Purchase #2	$38.44	9.312%	$42.0195	$42.02	$42.00	$42.00
Purchase #3	$52.52	5.715%	$55.5215	$55.52	$55.50	$55.50
Purchase #4	$114.75	7.619%	$123.4928	$123.49	$123.50	$123.50
Purchase #5	$145.76	9.489%	$159.5912	$159.59	$159.60	$159.60
Purchase #6	$194.45	12.784%	$219.3085	$219.31	$219.30	$219.30
Purchase #7	$194.88	7.294%	$209.0945	$209.09	$209.10	$209.10
7 purchase totals =	$804.24		$877.8782	$877.87	$877.85	$877.90