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	$29.71	6.193%	$31.5499	$31.55	$31.55	$31.50
Purchase #2	$122.82	8.635%	$133.4255	$133.43	$133.45	$133.40
Purchase #3	$127.39	8.156%	$137.7799	$137.78	$137.80	$137.80
Purchase #4	$9.94	3.387%	$10.2767	$10.28	$10.30	$10.30
Purchase #5	$52.58	3.825%	$54.5912	$54.59	$54.60	$54.60
Purchase #6	$169.35	5.328%	$178.373	$178.37	$178.35	$178.40
Purchase #7	$65.71	5.741%	$69.4824	$69.48	$69.50	$69.50
7 purchase totals =	$577.50		$615.4786	$615.48	$615.55	$615.50