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	$12.54	4.134%	$13.0584	$13.06	$13.05	$13.10
Purchase #2	$32.74	13.603%	$37.1936	$37.19	$37.20	$37.20
Purchase #3	$139.28	8.838%	$151.5896	$151.59	$151.60	$151.60
Purchase #4	$86.67	4.195%	$90.3058	$90.31	$90.30	$90.30
Purchase #5	$19.25	13.221%	$21.795	$21.80	$21.80	$21.80
Purchase #6	$232.56	12.325%	$261.223	$261.22	$261.20	$261.20
Purchase #7	$111.67	13.147%	$126.3513	$126.35	$126.35	$126.40
7 purchase totals =	$634.71		$701.5167	$701.52	$701.50	$701.60