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	$59.88	10.471%	$66.15	$66.15	$66.15	$66.20
Purchase #2	$10.56	4.473%	$11.0323	$11.03	$11.05	$11.00
Purchase #3	$211.90	8.244%	$229.369	$229.37	$229.35	$229.40
Purchase #4	$95.97	4.771%	$100.5487	$100.55	$100.55	$100.50
Purchase #5	$118.96	9.511%	$130.2743	$130.27	$130.25	$130.30
Purchase #6	$229.61	5.401%	$242.0112	$242.01	$242.00	$242.00
Purchase #7	$87.54	3.337%	$90.4612	$90.46	$90.45	$90.50
7 purchase totals =	$814.42		$869.8467	$869.84	$869.80	$869.90