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	$53.96	3.778%	$55.9986	$56.00	$56.00	$56.00
Purchase #2	$166.42	7.791%	$179.3858	$179.39	$179.40	$179.40
Purchase #3	$117.54	11.852%	$131.4708	$131.47	$131.45	$131.50
Purchase #4	$35.28	12.338%	$39.6328	$39.63	$39.65	$39.60
Purchase #5	$242.90	5.605%	$256.5145	$256.51	$256.50	$256.50
Purchase #6	$104.56	12.667%	$117.8046	$117.80	$117.80	$117.80
Purchase #7	$243.34	8.371%	$263.71	$263.71	$263.70	$263.70
7 purchase totals =	$964.00		$1,044.5171	$1,044.51	$1,044.50	$1,044.50