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	$208.29	5.432%	$219.6043	$219.60	$219.60	$219.60
Purchase #2	$142.72	13.859%	$162.4996	$162.50	$162.50	$162.50
Purchase #3	$117.82	9.718%	$129.2697	$129.27	$129.25	$129.30
Purchase #4	$223.43	3.370%	$230.9596	$230.96	$230.95	$231.00
Purchase #5	$58.28	5.217%	$61.3205	$61.32	$61.30	$61.30
Purchase #6	$155.86	8.162%	$168.5813	$168.58	$168.60	$168.60
Purchase #7	$144.99	3.639%	$150.2662	$150.27	$150.25	$150.30
7 purchase totals =	$1,051.39		$1,122.5012	$1,122.50	$1,122.45	$1,122.60