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	$205.25	11.480%	$228.8127	$228.81	$228.80	$228.80
Purchase #2	$187.84	6.712%	$200.4478	$200.45	$200.45	$200.40
Purchase #3	$79.25	12.726%	$89.3354	$89.34	$89.35	$89.30
Purchase #4	$97.71	13.631%	$111.0289	$111.03	$111.05	$111.00
Purchase #5	$45.38	13.316%	$51.4228	$51.42	$51.40	$51.40
Purchase #6	$179.30	7.674%	$193.0595	$193.06	$193.05	$193.10
Purchase #7	$124.99	8.493%	$135.6054	$135.61	$135.60	$135.60
7 purchase totals =	$919.72		$1,009.7125	$1,009.72	$1,009.70	$1,009.60