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	$48.33	7.249%	$51.8334	$51.83	$51.85	$51.80
Purchase #2	$241.54	10.397%	$266.6529	$266.65	$266.65	$266.70
Purchase #3	$245.38	8.283%	$265.7048	$265.70	$265.70	$265.70
Purchase #4	$152.51	12.164%	$171.0613	$171.06	$171.05	$171.10
Purchase #5	$127.98	7.376%	$137.4198	$137.42	$137.40	$137.40
Purchase #6	$144.86	12.184%	$162.5097	$162.51	$162.50	$162.50
Purchase #7	$69.90	11.801%	$78.1489	$78.15	$78.15	$78.10
7 purchase totals =	$1,030.50		$1,133.3308	$1,133.32	$1,133.30	$1,133.30