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	$36.36	12.306%	$40.8345	$40.83	$40.85	$40.80
Purchase #2	$244.88	5.685%	$258.8014	$258.80	$258.80	$258.80
Purchase #3	$157.83	11.153%	$175.4328	$175.43	$175.45	$175.40
Purchase #4	$121.72	5.420%	$128.3172	$128.32	$128.30	$128.30
Purchase #5	$107.63	3.630%	$111.537	$111.54	$111.55	$111.50
Purchase #6	$34.52	7.655%	$37.1625	$37.16	$37.15	$37.20
Purchase #7	$68.83	8.644%	$74.7797	$74.78	$74.80	$74.80
7 purchase totals =	$771.77		$826.8651	$826.86	$826.90	$826.80