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	$40.41	4.233%	$42.1206	$42.12	$42.10	$42.10
Purchase #2	$158.66	12.362%	$178.2735	$178.27	$178.25	$178.30
Purchase #3	$6.85	9.406%	$7.4943	$7.49	$7.50	$7.50
Purchase #4	$230.89	13.291%	$261.5776	$261.58	$261.60	$261.60
Purchase #5	$176.33	13.660%	$200.4167	$200.42	$200.40	$200.40
Purchase #6	$102.44	8.698%	$111.3502	$111.35	$111.35	$111.40
Purchase #7	$213.95	5.556%	$225.8371	$225.84	$225.85	$225.80
7 purchase totals =	$929.53		$1,027.0700	$1,027.07	$1,027.05	$1,027.10