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	$15.59	12.219%	$17.4949	$17.49	$17.50	$17.50
Purchase #2	$153.29	7.301%	$164.4817	$164.48	$164.50	$164.50
Purchase #3	$116.35	12.584%	$130.9915	$130.99	$131.00	$131.00
Purchase #4	$236.53	8.480%	$256.5877	$256.59	$256.60	$256.60
Purchase #5	$154.29	7.181%	$165.3696	$165.37	$165.35	$165.40
Purchase #6	$111.27	10.603%	$123.068	$123.07	$123.05	$123.10
Purchase #7	$241.28	6.489%	$256.9367	$256.94	$256.95	$256.90
7 purchase totals =	$1,028.60		$1,114.9301	$1,114.93	$1,114.95	$1,115.00