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	$21.50	6.340%	$22.8631	$22.86	$22.85	$22.90
Purchase #2	$82.71	9.543%	$90.603	$90.60	$90.60	$90.60
Purchase #3	$115.51	3.192%	$119.1971	$119.20	$119.20	$119.20
Purchase #4	$244.60	8.713%	$265.912	$265.91	$265.90	$265.90
Purchase #5	$46.25	9.239%	$50.523	$50.52	$50.50	$50.50
Purchase #6	$132.67	13.386%	$150.4292	$150.43	$150.45	$150.40
Purchase #7	$129.83	7.180%	$139.1518	$139.15	$139.15	$139.20
7 purchase totals =	$773.07		$838.6792	$838.67	$838.65	$838.70