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	$67.40	5.194%	$70.9008	$70.90	$70.90	$70.90
Purchase #2	$228.64	11.622%	$255.2125	$255.21	$255.20	$255.20
Purchase #3	$219.66	13.516%	$249.3492	$249.35	$249.35	$249.30
Purchase #4	$91.28	12.670%	$102.8452	$102.85	$102.85	$102.80
Purchase #5	$231.81	10.220%	$255.501	$255.50	$255.50	$255.50
Purchase #6	$12.53	11.795%	$14.0079	$14.01	$14.00	$14.00
Purchase #7	$54.45	9.260%	$59.4921	$59.49	$59.50	$59.50
7 purchase totals =	$905.77		$1,007.3087	$1,007.31	$1,007.30	$1,007.20