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	$118.56	4.109%	$123.4316	$123.43	$123.45	$123.40
Purchase #2	$145.45	9.186%	$158.811	$158.81	$158.80	$158.80
Purchase #3	$228.37	5.795%	$241.604	$241.60	$241.60	$241.60
Purchase #4	$213.43	12.493%	$240.0938	$240.09	$240.10	$240.10
Purchase #5	$5.61	4.850%	$5.8821	$5.88	$5.90	$5.90
Purchase #6	$62.27	8.772%	$67.7323	$67.73	$67.75	$67.70
Purchase #7	$56.28	10.561%	$62.2237	$62.22	$62.20	$62.20
7 purchase totals =	$829.97		$899.7785	$899.76	$899.80	$899.70