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	$231.74	3.252%	$239.2762	$239.28	$239.30	$239.30
Purchase #2	$96.78	8.598%	$105.1011	$105.10	$105.10	$105.10
Purchase #3	$72.48	8.414%	$78.5785	$78.58	$78.60	$78.60
Purchase #4	$164.46	13.750%	$187.0733	$187.07	$187.05	$187.10
Purchase #5	$74.45	5.672%	$78.6728	$78.67	$78.65	$78.70
Purchase #6	$130.31	9.354%	$142.4992	$142.50	$142.50	$142.50
Purchase #7	$208.53	13.519%	$236.7212	$236.72	$236.70	$236.70
7 purchase totals =	$978.75		$1,067.9223	$1,067.92	$1,067.90	$1,068.00