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	$38.97	9.176%	$42.5459	$42.55	$42.55	$42.50
Purchase #2	$27.91	10.747%	$30.9095	$30.91	$30.90	$30.90
Purchase #3	$57.26	13.274%	$64.8607	$64.86	$64.85	$64.90
Purchase #4	$160.81	3.553%	$166.5236	$166.52	$166.50	$166.50
Purchase #5	$231.32	11.733%	$258.4608	$258.46	$258.45	$258.50
Purchase #6	$95.86	7.377%	$102.9316	$102.93	$102.95	$102.90
Purchase #7	$40.41	12.269%	$45.3679	$45.37	$45.35	$45.40
7 purchase totals =	$652.54		$711.6000	$711.60	$711.55	$711.60