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	$201.39	11.647%	$224.8459	$224.85	$224.85	$224.80
Purchase #2	$139.80	13.863%	$159.1805	$159.18	$159.20	$159.20
Purchase #3	$139.39	9.800%	$153.0502	$153.05	$153.05	$153.10
Purchase #4	$27.61	3.123%	$28.4723	$28.47	$28.45	$28.50
Purchase #5	$19.81	10.244%	$21.8393	$21.84	$21.85	$21.80
Purchase #6	$103.99	7.201%	$111.4783	$111.48	$111.50	$111.50
Purchase #7	$177.60	7.858%	$191.5558	$191.56	$191.55	$191.60
7 purchase totals =	$809.59		$890.4223	$890.43	$890.45	$890.50