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	$125.39	11.708%	$140.0707	$140.07	$140.05	$140.10
Purchase #2	$37.41	5.636%	$39.5184	$39.52	$39.50	$39.50
Purchase #3	$165.82	10.642%	$183.4666	$183.47	$183.45	$183.50
Purchase #4	$215.58	5.591%	$227.6331	$227.63	$227.65	$227.60
Purchase #5	$229.71	5.510%	$242.367	$242.37	$242.35	$242.40
Purchase #6	$88.95	6.827%	$95.0226	$95.02	$95.00	$95.00
Purchase #7	$107.75	3.480%	$111.4997	$111.50	$111.50	$111.50
7 purchase totals =	$970.61		$1,039.5781	$1,039.58	$1,039.50	$1,039.60