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	$155.63	13.794%	$177.0976	$177.10	$177.10	$177.10
Purchase #2	$95.29	8.716%	$103.5955	$103.60	$103.60	$103.60
Purchase #3	$143.75	11.466%	$160.2324	$160.23	$160.25	$160.20
Purchase #4	$112.81	13.216%	$127.719	$127.72	$127.70	$127.70
Purchase #5	$136.39	5.469%	$143.8492	$143.85	$143.85	$143.80
Purchase #6	$154.58	13.355%	$175.2242	$175.22	$175.20	$175.20
Purchase #7	$228.94	13.493%	$259.8309	$259.83	$259.85	$259.80
7 purchase totals =	$1,027.39		$1,147.5488	$1,147.55	$1,147.55	$1,147.40