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	$238.86	12.588%	$268.9277	$268.93	$268.95	$268.90
Purchase #2	$113.35	9.853%	$124.5184	$124.52	$124.50	$124.50
Purchase #3	$105.97	5.487%	$111.7846	$111.78	$111.80	$111.80
Purchase #4	$178.68	4.709%	$187.094	$187.09	$187.10	$187.10
Purchase #5	$99.63	5.323%	$104.9333	$104.93	$104.95	$104.90
Purchase #6	$89.50	4.758%	$93.7584	$93.76	$93.75	$93.80
Purchase #7	$31.51	10.699%	$34.8813	$34.88	$34.90	$34.90
7 purchase totals =	$857.50		$925.8977	$925.89	$925.95	$925.90