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	$70.92	10.835%	$78.6042	$78.60	$78.60	$78.60
Purchase #2	$138.40	5.794%	$146.4189	$146.42	$146.40	$146.40
Purchase #3	$105.26	7.585%	$113.244	$113.24	$113.25	$113.20
Purchase #4	$111.28	11.241%	$123.789	$123.79	$123.80	$123.80
Purchase #5	$52.59	5.557%	$55.5124	$55.51	$55.50	$55.50
Purchase #6	$87.53	8.389%	$94.8729	$94.87	$94.85	$94.90
Purchase #7	$210.89	5.438%	$222.3582	$222.36	$222.35	$222.40
7 purchase totals =	$776.87		$834.7996	$834.79	$834.75	$834.80