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	$80.70	3.422%	$83.4616	$83.46	$83.45	$83.50
Purchase #2	$104.83	6.688%	$111.841	$111.84	$111.85	$111.80
Purchase #3	$198.87	12.617%	$223.9614	$223.96	$223.95	$224.00
Purchase #4	$100.64	10.355%	$111.0613	$111.06	$111.05	$111.10
Purchase #5	$132.89	13.115%	$150.3185	$150.32	$150.30	$150.30
Purchase #6	$162.52	3.280%	$167.8507	$167.85	$167.85	$167.90
Purchase #7	$141.71	6.506%	$150.9297	$150.93	$150.95	$150.90
7 purchase totals =	$922.16		$999.4242	$999.42	$999.40	$999.50