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	$39.51	8.460%	$42.8525	$42.85	$42.85	$42.90
Purchase #2	$162.53	3.665%	$168.4867	$168.49	$168.50	$168.50
Purchase #3	$199.69	11.255%	$222.1651	$222.17	$222.15	$222.20
Purchase #4	$226.68	12.400%	$254.7883	$254.79	$254.80	$254.80
Purchase #5	$39.30	9.649%	$43.0921	$43.09	$43.10	$43.10
Purchase #6	$11.35	5.305%	$11.9521	$11.95	$11.95	$12.00
Purchase #7	$109.40	7.795%	$117.9277	$117.93	$117.95	$117.90
7 purchase totals =	$788.46		$861.2645	$861.27	$861.30	$861.40