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	$186.90	5.142%	$196.5104	$196.51	$196.50	$196.50
Purchase #2	$51.25	9.821%	$56.2833	$56.28	$56.30	$56.30
Purchase #3	$175.66	4.612%	$183.7614	$183.76	$183.75	$183.80
Purchase #4	$222.53	12.795%	$251.0027	$251.00	$251.00	$251.00
Purchase #5	$116.50	13.504%	$132.2322	$132.23	$132.25	$132.20
Purchase #6	$72.41	13.363%	$82.0861	$82.09	$82.10	$82.10
Purchase #7	$232.32	4.473%	$242.7117	$242.71	$242.70	$242.70
7 purchase totals =	$1,057.57		$1,144.5878	$1,144.58	$1,144.60	$1,144.60