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	$239.72	12.336%	$269.2919	$269.29	$269.30	$269.30
Purchase #2	$127.38	3.705%	$132.0994	$132.10	$132.10	$132.10
Purchase #3	$196.31	13.256%	$222.3329	$222.33	$222.35	$222.30
Purchase #4	$215.45	5.662%	$227.6488	$227.65	$227.65	$227.60
Purchase #5	$30.85	6.480%	$32.8491	$32.85	$32.85	$32.80
Purchase #6	$163.56	13.532%	$185.6929	$185.69	$185.70	$185.70
Purchase #7	$9.31	7.430%	$10.0017	$10.00	$10.00	$10.00
7 purchase totals =	$982.58		$1,079.9167	$1,079.91	$1,079.95	$1,079.80