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	$99.71	11.808%	$111.4838	$111.48	$111.50	$111.50
Purchase #2	$178.92	3.313%	$184.8476	$184.85	$184.85	$184.80
Purchase #3	$215.72	8.840%	$234.7896	$234.79	$234.80	$234.80
Purchase #4	$42.42	6.762%	$45.2884	$45.29	$45.30	$45.30
Purchase #5	$98.28	12.619%	$110.682	$110.68	$110.70	$110.70
Purchase #6	$192.51	12.156%	$215.9115	$215.91	$215.90	$215.90
Purchase #7	$57.50	4.853%	$60.2905	$60.29	$60.30	$60.30
7 purchase totals =	$885.06		$963.2934	$963.29	$963.35	$963.30