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	$82.39	9.684%	$90.3686	$90.37	$90.35	$90.40
Purchase #2	$55.32	4.142%	$57.6114	$57.61	$57.60	$57.60
Purchase #3	$81.29	11.300%	$90.4758	$90.48	$90.50	$90.50
Purchase #4	$170.55	13.416%	$193.431	$193.43	$193.45	$193.40
Purchase #5	$92.70	11.244%	$103.1232	$103.12	$103.10	$103.10
Purchase #6	$24.40	4.513%	$25.5012	$25.50	$25.50	$25.50
Purchase #7	$64.46	5.774%	$68.1819	$68.18	$68.20	$68.20
7 purchase totals =	$571.11		$628.6931	$628.69	$628.70	$628.70