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	$40.88	11.613%	$45.6274	$45.63	$45.65	$45.60
Purchase #2	$120.29	10.861%	$133.3547	$133.35	$133.35	$133.40
Purchase #3	$49.77	8.589%	$54.0447	$54.04	$54.05	$54.00
Purchase #4	$208.59	7.762%	$224.7808	$224.78	$224.80	$224.80
Purchase #5	$103.55	3.672%	$107.3524	$107.35	$107.35	$107.40
Purchase #6	$131.56	8.170%	$142.3085	$142.31	$142.30	$142.30
Purchase #7	$103.56	8.740%	$112.6111	$112.61	$112.60	$112.60
7 purchase totals =	$758.20		$820.0796	$820.07	$820.10	$820.10