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	$111.95	10.386%	$123.5771	$123.58	$123.60	$123.60
Purchase #2	$147.80	13.136%	$167.215	$167.22	$167.20	$167.20
Purchase #3	$50.75	9.476%	$55.5591	$55.56	$55.55	$55.60
Purchase #4	$102.35	11.394%	$114.0118	$114.01	$114.00	$114.00
Purchase #5	$63.58	5.866%	$67.3096	$67.31	$67.30	$67.30
Purchase #6	$220.78	6.504%	$235.1395	$235.14	$235.15	$235.10
Purchase #7	$49.52	13.220%	$56.0665	$56.07	$56.05	$56.10
7 purchase totals =	$746.73		$818.8786	$818.89	$818.85	$818.90