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	$250.42	12.458%	$281.6173	$281.62	$281.60	$281.60
Purchase #2	$155.67	5.395%	$164.0684	$164.07	$164.05	$164.10
Purchase #3	$29.87	3.866%	$31.0248	$31.02	$31.00	$31.00
Purchase #4	$38.82	12.826%	$43.7991	$43.80	$43.80	$43.80
Purchase #5	$148.36	4.650%	$155.2587	$155.26	$155.25	$155.30
Purchase #6	$187.36	4.832%	$196.4132	$196.41	$196.40	$196.40
Purchase #7	$129.48	5.852%	$137.0572	$137.06	$137.05	$137.10
7 purchase totals =	$939.98		$1,009.2387	$1,009.24	$1,009.15	$1,009.30