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	$171.73	9.185%	$187.5034	$187.50	$187.50	$187.50
Purchase #2	$130.61	13.765%	$148.5885	$148.59	$148.60	$148.60
Purchase #3	$140.47	5.698%	$148.474	$148.47	$148.45	$148.50
Purchase #4	$235.43	6.162%	$249.9372	$249.94	$249.95	$249.90
Purchase #5	$11.58	6.777%	$12.3648	$12.36	$12.35	$12.40
Purchase #6	$99.68	13.261%	$112.8986	$112.90	$112.90	$112.90
Purchase #7	$230.29	9.409%	$251.958	$251.96	$251.95	$252.00
7 purchase totals =	$1,019.79		$1,111.7245	$1,111.72	$1,111.70	$1,111.80