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	$11.35	12.736%	$12.7955	$12.80	$12.80	$12.80
Purchase #2	$106.46	11.209%	$118.3931	$118.39	$118.40	$118.40
Purchase #3	$75.94	13.204%	$85.9671	$85.97	$85.95	$86.00
Purchase #4	$141.91	9.752%	$155.7491	$155.75	$155.75	$155.70
Purchase #5	$92.69	11.670%	$103.5069	$103.51	$103.50	$103.50
Purchase #6	$63.71	13.206%	$72.1235	$72.12	$72.10	$72.10
Purchase #7	$12.67	10.203%	$13.9627	$13.96	$13.95	$14.00
7 purchase totals =	$504.73		$562.4979	$562.50	$562.45	$562.50