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	$12.44	6.481%	$13.2462	$13.25	$13.25	$13.20
Purchase #2	$231.93	7.640%	$249.6495	$249.65	$249.65	$249.60
Purchase #3	$172.58	10.733%	$191.103	$191.10	$191.10	$191.10
Purchase #4	$13.40	6.161%	$14.2256	$14.23	$14.25	$14.20
Purchase #5	$150.40	10.763%	$166.5876	$166.59	$166.60	$166.60
Purchase #6	$191.31	12.169%	$214.5905	$214.59	$214.60	$214.60
Purchase #7	$205.92	5.360%	$216.9573	$216.96	$216.95	$217.00
7 purchase totals =	$977.98		$1,066.3597	$1,066.37	$1,066.40	$1,066.30