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	$21.70	7.681%	$23.3668	$23.37	$23.35	$23.40
Purchase #2	$97.55	3.445%	$100.9106	$100.91	$100.90	$100.90
Purchase #3	$133.90	9.706%	$146.8963	$146.90	$146.90	$146.90
Purchase #4	$203.86	13.692%	$231.7725	$231.77	$231.75	$231.80
Purchase #5	$91.89	13.318%	$104.1279	$104.13	$104.15	$104.10
Purchase #6	$139.81	13.372%	$158.5054	$158.51	$158.50	$158.50
Purchase #7	$100.63	11.393%	$112.0948	$112.09	$112.10	$112.10
7 purchase totals =	$789.34		$877.6743	$877.68	$877.65	$877.70