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	$29.93	5.594%	$31.6043	$31.60	$31.60	$31.60
Purchase #2	$162.63	12.622%	$183.1572	$183.16	$183.15	$183.20
Purchase #3	$124.52	9.423%	$136.2535	$136.25	$136.25	$136.30
Purchase #4	$205.41	6.534%	$218.8315	$218.83	$218.85	$218.80
Purchase #5	$80.42	11.633%	$89.7753	$89.78	$89.80	$89.80
Purchase #6	$116.51	10.188%	$128.38	$128.38	$128.40	$128.40
Purchase #7	$128.30	5.578%	$135.4566	$135.46	$135.45	$135.50
7 purchase totals =	$847.72		$923.4584	$923.46	$923.50	$923.60