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	$203.78	13.655%	$231.6062	$231.61	$231.60	$231.60
Purchase #2	$227.59	6.574%	$242.5518	$242.55	$242.55	$242.60
Purchase #3	$134.47	7.509%	$144.5674	$144.57	$144.55	$144.60
Purchase #4	$100.25	9.186%	$109.459	$109.46	$109.45	$109.50
Purchase #5	$188.52	10.837%	$208.9499	$208.95	$208.95	$208.90
Purchase #6	$174.69	3.236%	$180.343	$180.34	$180.35	$180.30
Purchase #7	$222.87	8.733%	$242.3332	$242.33	$242.35	$242.30
7 purchase totals =	$1,252.17		$1,359.8105	$1,359.81	$1,359.80	$1,359.80