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	$48.48	10.233%	$53.441	$53.44	$53.45	$53.40
Purchase #2	$68.65	13.803%	$78.1258	$78.13	$78.15	$78.10
Purchase #3	$76.42	7.547%	$82.1874	$82.19	$82.20	$82.20
Purchase #4	$18.94	9.611%	$20.7603	$20.76	$20.75	$20.80
Purchase #5	$199.45	10.808%	$221.0066	$221.01	$221.00	$221.00
Purchase #6	$207.29	11.681%	$231.5035	$231.50	$231.50	$231.50
Purchase #7	$122.85	7.299%	$131.8168	$131.82	$131.80	$131.80
7 purchase totals =	$742.08		$818.8414	$818.85	$818.85	$818.80