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	$132.25	6.297%	$140.5778	$140.58	$140.60	$140.60
Purchase #2	$169.64	10.637%	$187.6846	$187.68	$187.70	$187.70
Purchase #3	$45.73	4.841%	$47.9438	$47.94	$47.95	$47.90
Purchase #4	$86.72	4.348%	$90.4906	$90.49	$90.50	$90.50
Purchase #5	$27.50	3.789%	$28.542	$28.54	$28.55	$28.50
Purchase #6	$219.50	10.105%	$241.6805	$241.68	$241.70	$241.70
Purchase #7	$168.61	8.210%	$182.4529	$182.45	$182.45	$182.50
7 purchase totals =	$849.95		$919.3722	$919.36	$919.45	$919.40