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	$12.33	10.680%	$13.6468	$13.65	$13.65	$13.60
Purchase #2	$89.98	10.543%	$99.4666	$99.47	$99.45	$99.50
Purchase #3	$154.79	11.634%	$172.7983	$172.80	$172.80	$172.80
Purchase #4	$196.43	11.452%	$218.9252	$218.93	$218.95	$218.90
Purchase #5	$14.68	11.687%	$16.3957	$16.40	$16.40	$16.40
Purchase #6	$114.25	7.777%	$123.1352	$123.14	$123.15	$123.10
Purchase #7	$50.85	3.308%	$52.5321	$52.53	$52.55	$52.50
7 purchase totals =	$633.31		$696.8999	$696.92	$696.95	$696.80