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	$172.80	8.338%	$187.2081	$187.21	$187.20	$187.20
Purchase #2	$171.62	9.207%	$187.4211	$187.42	$187.40	$187.40
Purchase #3	$89.34	10.626%	$98.8333	$98.83	$98.85	$98.80
Purchase #4	$230.29	9.189%	$251.4513	$251.45	$251.45	$251.50
Purchase #5	$187.63	13.274%	$212.536	$212.54	$212.55	$212.50
Purchase #6	$90.35	10.714%	$100.0301	$100.03	$100.05	$100.00
Purchase #7	$103.46	9.794%	$113.5929	$113.59	$113.60	$113.60
7 purchase totals =	$1,045.49		$1,151.0728	$1,151.07	$1,151.10	$1,151.00