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	$48.85	10.373%	$53.9172	$53.92	$53.90	$53.90
Purchase #2	$217.58	11.474%	$242.5451	$242.55	$242.55	$242.50
Purchase #3	$54.83	11.421%	$61.0921	$61.09	$61.10	$61.10
Purchase #4	$90.93	11.595%	$101.4733	$101.47	$101.45	$101.50
Purchase #5	$117.63	4.429%	$122.8398	$122.84	$122.85	$122.80
Purchase #6	$146.63	4.258%	$152.8735	$152.87	$152.85	$152.90
Purchase #7	$112.36	12.774%	$126.7129	$126.71	$126.70	$126.70
7 purchase totals =	$788.81		$861.4539	$861.45	$861.40	$861.40