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	$227.63	4.230%	$237.2587	$237.26	$237.25	$237.30
Purchase #2	$106.26	3.148%	$109.6051	$109.61	$109.60	$109.60
Purchase #3	$89.50	12.632%	$100.8056	$100.81	$100.80	$100.80
Purchase #4	$10.42	7.628%	$11.2148	$11.21	$11.20	$11.20
Purchase #5	$250.43	11.792%	$279.9607	$279.96	$279.95	$280.00
Purchase #6	$43.39	8.188%	$46.9428	$46.94	$46.95	$46.90
Purchase #7	$148.59	3.444%	$153.7074	$153.71	$153.70	$153.70
7 purchase totals =	$876.22		$939.4951	$939.50	$939.45	$939.50