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	$100.31	12.131%	$112.4786	$112.48	$112.50	$112.50
Purchase #2	$110.96	11.624%	$123.858	$123.86	$123.85	$123.90
Purchase #3	$176.45	10.760%	$195.436	$195.44	$195.45	$195.40
Purchase #4	$57.71	8.108%	$62.3891	$62.39	$62.40	$62.40
Purchase #5	$132.42	7.487%	$142.3343	$142.33	$142.35	$142.30
Purchase #6	$246.60	3.696%	$255.7143	$255.71	$255.70	$255.70
Purchase #7	$10.35	8.103%	$11.1887	$11.19	$11.20	$11.20
7 purchase totals =	$834.80		$903.3990	$903.40	$903.45	$903.40