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	$244.40	10.748%	$270.6681	$270.67	$270.65	$270.70
Purchase #2	$120.42	13.528%	$136.7104	$136.71	$136.70	$136.70
Purchase #3	$80.67	3.289%	$83.3232	$83.32	$83.30	$83.30
Purchase #4	$73.25	12.675%	$82.5344	$82.53	$82.55	$82.50
Purchase #5	$179.37	6.710%	$191.4057	$191.41	$191.40	$191.40
Purchase #6	$155.48	11.596%	$173.5095	$173.51	$173.50	$173.50
Purchase #7	$16.35	10.682%	$18.0965	$18.10	$18.10	$18.10
7 purchase totals =	$869.94		$956.2478	$956.25	$956.20	$956.20