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	$45.86	13.292%	$51.9557	$51.96	$51.95	$52.00
Purchase #2	$52.79	9.513%	$57.8119	$57.81	$57.80	$57.80
Purchase #3	$108.65	13.714%	$123.5503	$123.55	$123.55	$123.60
Purchase #4	$144.38	12.739%	$162.7726	$162.77	$162.75	$162.80
Purchase #5	$148.74	4.602%	$155.585	$155.59	$155.60	$155.60
Purchase #6	$70.85	8.584%	$76.9318	$76.93	$76.95	$76.90
Purchase #7	$70.62	8.698%	$76.7625	$76.76	$76.75	$76.80
7 purchase totals =	$641.89		$705.3698	$705.37	$705.35	$705.50