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	$47.25	13.633%	$53.6916	$53.69	$53.70	$53.70
Purchase #2	$12.86	9.803%	$14.1207	$14.12	$14.10	$14.10
Purchase #3	$138.30	8.667%	$150.2865	$150.29	$150.30	$150.30
Purchase #4	$10.94	3.356%	$11.3071	$11.31	$11.30	$11.30
Purchase #5	$158.59	7.712%	$170.8205	$170.82	$170.80	$170.80
Purchase #6	$134.29	10.214%	$148.0064	$148.01	$148.00	$148.00
Purchase #7	$80.67	11.373%	$89.8446	$89.84	$89.85	$89.80
7 purchase totals =	$582.90		$638.0774	$638.08	$638.05	$638.00