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	$46.53	12.274%	$52.2411	$52.24	$52.25	$52.20
Purchase #2	$41.69	3.542%	$43.1667	$43.17	$43.15	$43.20
Purchase #3	$111.28	4.733%	$116.5469	$116.55	$116.55	$116.50
Purchase #4	$102.41	13.699%	$116.4391	$116.44	$116.45	$116.40
Purchase #5	$69.56	12.462%	$78.2286	$78.23	$78.25	$78.20
Purchase #6	$217.25	9.364%	$237.5933	$237.59	$237.60	$237.60
Purchase #7	$12.29	12.307%	$13.8025	$13.80	$13.80	$13.80
7 purchase totals =	$601.01		$658.0182	$658.02	$658.05	$657.90