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	$8.51	3.114%	$8.775	$8.78	$8.80	$8.80
Purchase #2	$104.52	6.562%	$111.3786	$111.38	$111.40	$111.40
Purchase #3	$100.55	12.239%	$112.8563	$112.86	$112.85	$112.90
Purchase #4	$46.58	11.380%	$51.8808	$51.88	$51.90	$51.90
Purchase #5	$72.37	5.701%	$76.4958	$76.50	$76.50	$76.50
Purchase #6	$173.52	7.470%	$186.4819	$186.48	$186.50	$186.50
Purchase #7	$50.29	12.571%	$56.612	$56.61	$56.60	$56.60
7 purchase totals =	$556.34		$604.4804	$604.49	$604.55	$604.60