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	$106.93	10.233%	$117.8721	$117.87	$117.85	$117.90
Purchase #2	$130.31	12.667%	$146.8164	$146.82	$146.80	$146.80
Purchase #3	$153.71	8.333%	$166.5187	$166.52	$166.50	$166.50
Purchase #4	$84.54	13.509%	$95.9605	$95.96	$95.95	$96.00
Purchase #5	$15.73	11.235%	$17.4973	$17.50	$17.50	$17.50
Purchase #6	$35.28	6.341%	$37.5171	$37.52	$37.50	$37.50
Purchase #7	$80.94	12.304%	$90.8989	$90.90	$90.90	$90.90
7 purchase totals =	$607.44		$673.0810	$673.09	$673.00	$673.10