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	$8.49	9.451%	$9.2924	$9.29	$9.30	$9.30
Purchase #2	$120.85	7.193%	$129.5427	$129.54	$129.55	$129.50
Purchase #3	$197.47	12.602%	$222.3552	$222.36	$222.35	$222.40
Purchase #4	$118.84	8.127%	$128.4981	$128.50	$128.50	$128.50
Purchase #5	$80.78	10.271%	$89.0769	$89.08	$89.10	$89.10
Purchase #6	$228.83	12.820%	$258.166	$258.17	$258.15	$258.20
Purchase #7	$56.76	4.829%	$59.5009	$59.50	$59.50	$59.50
7 purchase totals =	$812.02		$896.4322	$896.44	$896.45	$896.50