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	$26.36	11.647%	$29.4301	$29.43	$29.45	$29.40
Purchase #2	$167.69	10.299%	$184.9604	$184.96	$184.95	$185.00
Purchase #3	$148.73	6.388%	$158.2309	$158.23	$158.25	$158.20
Purchase #4	$132.39	10.572%	$146.3863	$146.39	$146.40	$146.40
Purchase #5	$47.78	8.724%	$51.9483	$51.95	$51.95	$51.90
Purchase #6	$29.30	7.520%	$31.5034	$31.50	$31.50	$31.50
Purchase #7	$78.36	5.755%	$82.8696	$82.87	$82.85	$82.90
7 purchase totals =	$630.61		$685.3290	$685.33	$685.35	$685.30