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	$17.57	6.545%	$18.72	$18.72	$18.70	$18.70
Purchase #2	$97.39	12.274%	$109.3436	$109.34	$109.35	$109.30
Purchase #3	$85.59	5.485%	$90.2846	$90.28	$90.30	$90.30
Purchase #4	$247.60	11.138%	$275.1777	$275.18	$275.20	$275.20
Purchase #5	$81.99	6.111%	$87.0004	$87.00	$87.00	$87.00
Purchase #6	$141.80	9.835%	$155.746	$155.75	$155.75	$155.70
Purchase #7	$124.80	5.377%	$131.5105	$131.51	$131.50	$131.50
7 purchase totals =	$796.74		$867.7828	$867.78	$867.80	$867.70