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	$107.86	4.311%	$112.5098	$112.51	$112.50	$112.50
Purchase #2	$131.80	10.841%	$146.0884	$146.09	$146.10	$146.10
Purchase #3	$33.62	11.533%	$37.4974	$37.50	$37.50	$37.50
Purchase #4	$21.91	7.848%	$23.6295	$23.63	$23.65	$23.60
Purchase #5	$88.86	13.106%	$100.506	$100.51	$100.50	$100.50
Purchase #6	$100.92	3.107%	$104.0556	$104.06	$104.05	$104.10
Purchase #7	$123.76	13.229%	$140.1322	$140.13	$140.15	$140.10
7 purchase totals =	$608.73		$664.4189	$664.43	$664.45	$664.40