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	$38.83	12.255%	$43.5886	$43.59	$43.60	$43.60
Purchase #2	$61.28	6.870%	$65.4899	$65.49	$65.50	$65.50
Purchase #3	$40.34	13.625%	$45.8363	$45.84	$45.85	$45.80
Purchase #4	$165.54	10.599%	$183.0856	$183.09	$183.10	$183.10
Purchase #5	$6.96	7.274%	$7.4663	$7.47	$7.45	$7.50
Purchase #6	$54.83	12.671%	$61.7775	$61.78	$61.80	$61.80
Purchase #7	$146.35	3.132%	$150.9337	$150.93	$150.95	$150.90
7 purchase totals =	$514.13		$558.1779	$558.19	$558.25	$558.20