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	$244.67	11.616%	$273.0909	$273.09	$273.10	$273.10
Purchase #2	$93.52	7.167%	$100.2226	$100.22	$100.20	$100.20
Purchase #3	$46.98	9.656%	$51.5164	$51.52	$51.50	$51.50
Purchase #4	$75.64	12.386%	$85.0088	$85.01	$85.00	$85.00
Purchase #5	$210.75	3.211%	$217.5172	$217.52	$217.50	$217.50
Purchase #6	$66.39	5.191%	$69.8363	$69.84	$69.85	$69.80
Purchase #7	$155.38	6.432%	$165.374	$165.37	$165.35	$165.40
7 purchase totals =	$893.33		$962.5662	$962.57	$962.50	$962.50