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	$228.48	5.563%	$241.1903	$241.19	$241.20	$241.20
Purchase #2	$212.54	13.358%	$240.9311	$240.93	$240.95	$240.90
Purchase #3	$234.89	8.668%	$255.2503	$255.25	$255.25	$255.30
Purchase #4	$131.30	10.134%	$144.6059	$144.61	$144.60	$144.60
Purchase #5	$113.45	8.696%	$123.3156	$123.32	$123.30	$123.30
Purchase #6	$53.77	3.324%	$55.5573	$55.56	$55.55	$55.60
Purchase #7	$191.59	12.621%	$215.7706	$215.77	$215.75	$215.80
7 purchase totals =	$1,166.02		$1,276.6211	$1,276.63	$1,276.60	$1,276.70