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	$138.33	11.791%	$154.6405	$154.64	$154.65	$154.60
Purchase #2	$23.56	3.528%	$24.3912	$24.39	$24.40	$24.40
Purchase #3	$130.89	11.228%	$145.5863	$145.59	$145.60	$145.60
Purchase #4	$151.31	8.849%	$164.6994	$164.70	$164.70	$164.70
Purchase #5	$80.93	9.787%	$88.8506	$88.85	$88.85	$88.90
Purchase #6	$52.38	13.495%	$59.4487	$59.45	$59.45	$59.40
Purchase #7	$192.79	6.822%	$205.9421	$205.94	$205.95	$205.90
7 purchase totals =	$770.19		$843.5588	$843.56	$843.60	$843.50