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	$24.73	10.747%	$27.3877	$27.39	$27.40	$27.40
Purchase #2	$180.30	10.776%	$199.7291	$199.73	$199.75	$199.70
Purchase #3	$107.37	3.765%	$111.4125	$111.41	$111.40	$111.40
Purchase #4	$66.28	11.533%	$73.9241	$73.92	$73.90	$73.90
Purchase #5	$141.45	4.597%	$147.9525	$147.95	$147.95	$148.00
Purchase #6	$107.77	12.403%	$121.1367	$121.14	$121.15	$121.10
Purchase #7	$128.83	12.147%	$144.479	$144.48	$144.50	$144.50
7 purchase totals =	$756.73		$826.0216	$826.02	$826.05	$826.00