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	$10.45	12.800%	$11.7876	$11.79	$11.80	$11.80
Purchase #2	$38.91	4.773%	$40.7672	$40.77	$40.75	$40.80
Purchase #3	$148.75	8.742%	$161.7537	$161.75	$161.75	$161.80
Purchase #4	$87.40	3.248%	$90.2388	$90.24	$90.25	$90.20
Purchase #5	$86.65	4.274%	$90.3534	$90.35	$90.35	$90.40
Purchase #6	$209.25	10.111%	$230.4073	$230.41	$230.40	$230.40
Purchase #7	$51.38	4.578%	$53.7322	$53.73	$53.75	$53.70
7 purchase totals =	$632.79		$679.0402	$679.04	$679.05	$679.10