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	$26.41	11.437%	$29.4305	$29.43	$29.45	$29.40
Purchase #2	$110.48	11.825%	$123.5443	$123.54	$123.55	$123.50
Purchase #3	$95.71	9.216%	$104.5306	$104.53	$104.55	$104.50
Purchase #4	$186.59	10.322%	$205.8498	$205.85	$205.85	$205.80
Purchase #5	$176.70	7.592%	$190.1151	$190.12	$190.10	$190.10
Purchase #6	$242.83	8.136%	$262.5866	$262.59	$262.60	$262.60
Purchase #7	$27.68	6.630%	$29.5152	$29.52	$29.50	$29.50
7 purchase totals =	$866.40		$945.5721	$945.58	$945.60	$945.40