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	$20.57	6.219%	$21.8492	$21.85	$21.85	$21.80
Purchase #2	$87.44	3.362%	$90.3797	$90.38	$90.40	$90.40
Purchase #3	$144.37	9.781%	$158.4908	$158.49	$158.50	$158.50
Purchase #4	$184.88	11.527%	$206.1911	$206.19	$206.20	$206.20
Purchase #5	$144.42	5.815%	$152.818	$152.82	$152.80	$152.80
Purchase #6	$104.88	12.105%	$117.5757	$117.58	$117.60	$117.60
Purchase #7	$75.44	7.137%	$80.8242	$80.82	$80.80	$80.80
7 purchase totals =	$762.00		$828.1287	$828.13	$828.15	$828.10