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	$239.97	11.860%	$268.4304	$268.43	$268.45	$268.40
Purchase #2	$118.34	4.373%	$123.515	$123.52	$123.50	$123.50
Purchase #3	$51.63	6.387%	$54.9276	$54.93	$54.95	$54.90
Purchase #4	$239.61	13.376%	$271.6602	$271.66	$271.65	$271.70
Purchase #5	$249.95	11.431%	$278.5218	$278.52	$278.50	$278.50
Purchase #6	$66.67	10.667%	$73.7817	$73.78	$73.80	$73.80
Purchase #7	$75.59	12.667%	$85.165	$85.17	$85.15	$85.20
7 purchase totals =	$1,041.76		$1,156.0017	$1,156.01	$1,156.00	$1,156.00