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	$243.52	11.394%	$271.2667	$271.27	$271.25	$271.30
Purchase #2	$113.87	4.183%	$118.6332	$118.63	$118.65	$118.60
Purchase #3	$112.27	5.569%	$118.5223	$118.52	$118.50	$118.50
Purchase #4	$116.93	13.209%	$132.3753	$132.38	$132.40	$132.40
Purchase #5	$191.49	8.821%	$208.3813	$208.38	$208.40	$208.40
Purchase #6	$169.91	7.837%	$183.2258	$183.23	$183.25	$183.20
Purchase #7	$229.31	11.838%	$256.4557	$256.46	$256.45	$256.50
7 purchase totals =	$1,177.30		$1,288.8603	$1,288.87	$1,288.90	$1,288.90