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	$166.75	11.473%	$185.8812	$185.88	$185.90	$185.90
Purchase #2	$65.63	9.816%	$72.0722	$72.07	$72.05	$72.10
Purchase #3	$248.99	12.296%	$279.6058	$279.61	$279.60	$279.60
Purchase #4	$210.68	8.696%	$229.0007	$229.00	$229.00	$229.00
Purchase #5	$19.66	4.188%	$20.4834	$20.48	$20.50	$20.50
Purchase #6	$43.88	7.746%	$47.2789	$47.28	$47.30	$47.30
Purchase #7	$168.45	6.161%	$178.8282	$178.83	$178.85	$178.80
7 purchase totals =	$924.04		$1,013.1504	$1,013.15	$1,013.20	$1,013.20