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	$77.38	11.138%	$85.9986	$86.00	$86.00	$86.00
Purchase #2	$52.38	13.694%	$59.5529	$59.55	$59.55	$59.60
Purchase #3	$82.54	6.540%	$87.9381	$87.94	$87.95	$87.90
Purchase #4	$48.70	9.367%	$53.2617	$53.26	$53.25	$53.30
Purchase #5	$125.54	13.456%	$142.4327	$142.43	$142.45	$142.40
Purchase #6	$139.96	8.483%	$151.8328	$151.83	$151.85	$151.80
Purchase #7	$246.54	4.782%	$258.3295	$258.33	$258.35	$258.30
7 purchase totals =	$773.04		$839.3463	$839.34	$839.40	$839.30