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	$164.78	12.704%	$185.7137	$185.71	$185.70	$185.70
Purchase #2	$82.43	6.359%	$87.6717	$87.67	$87.65	$87.70
Purchase #3	$118.64	7.308%	$127.3102	$127.31	$127.30	$127.30
Purchase #4	$95.85	13.277%	$108.576	$108.58	$108.60	$108.60
Purchase #5	$75.71	3.364%	$78.2569	$78.26	$78.25	$78.30
Purchase #6	$31.45	8.188%	$34.0251	$34.03	$34.05	$34.00
Purchase #7	$182.58	9.136%	$199.2605	$199.26	$199.25	$199.30
7 purchase totals =	$751.44		$820.8141	$820.82	$820.80	$820.90