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	$139.58	13.471%	$158.3828	$158.38	$158.40	$158.40
Purchase #2	$92.58	12.130%	$103.81	$103.81	$103.80	$103.80
Purchase #3	$208.46	4.513%	$217.8678	$217.87	$217.85	$217.90
Purchase #4	$129.78	10.592%	$143.5263	$143.53	$143.55	$143.50
Purchase #5	$205.31	8.650%	$223.0693	$223.07	$223.05	$223.10
Purchase #6	$131.57	10.744%	$145.7059	$145.71	$145.70	$145.70
Purchase #7	$60.94	11.709%	$68.0755	$68.08	$68.10	$68.10
7 purchase totals =	$968.22		$1,060.4376	$1,060.45	$1,060.45	$1,060.50