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	$140.85	13.236%	$159.4929	$159.49	$159.50	$159.50
Purchase #2	$210.88	12.584%	$237.4171	$237.42	$237.40	$237.40
Purchase #3	$177.45	7.845%	$191.371	$191.37	$191.35	$191.40
Purchase #4	$85.60	5.727%	$90.5023	$90.50	$90.50	$90.50
Purchase #5	$102.81	7.765%	$110.7932	$110.79	$110.80	$110.80
Purchase #6	$45.94	9.744%	$50.4164	$50.42	$50.40	$50.40
Purchase #7	$207.35	8.811%	$225.6196	$225.62	$225.60	$225.60
7 purchase totals =	$970.88		$1,065.6125	$1,065.61	$1,065.55	$1,065.60