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	$168.38	12.710%	$189.7811	$189.78	$189.80	$189.80
Purchase #2	$165.48	13.384%	$187.6278	$187.63	$187.65	$187.60
Purchase #3	$36.81	10.634%	$40.7244	$40.72	$40.70	$40.70
Purchase #4	$124.76	6.439%	$132.7933	$132.79	$132.80	$132.80
Purchase #5	$113.66	4.209%	$118.4439	$118.44	$118.45	$118.40
Purchase #6	$68.86	7.218%	$73.8303	$73.83	$73.85	$73.80
Purchase #7	$73.57	6.139%	$78.0865	$78.09	$78.10	$78.10
7 purchase totals =	$751.52		$821.2873	$821.28	$821.35	$821.20