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	$52.76	9.521%	$57.7833	$57.78	$57.80	$57.80
Purchase #2	$198.34	12.261%	$222.6585	$222.66	$222.65	$222.70
Purchase #3	$106.54	6.547%	$113.5152	$113.52	$113.50	$113.50
Purchase #4	$246.59	13.772%	$280.5504	$280.55	$280.55	$280.60
Purchase #5	$18.25	11.137%	$20.2825	$20.28	$20.30	$20.30
Purchase #6	$152.64	4.125%	$158.9364	$158.94	$158.95	$158.90
Purchase #7	$63.43	5.724%	$67.0607	$67.06	$67.05	$67.10
7 purchase totals =	$838.55		$920.7870	$920.79	$920.80	$920.90