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	$81.39	6.396%	$86.5957	$86.60	$86.60	$86.60
Purchase #2	$87.65	11.241%	$97.5027	$97.50	$97.50	$97.50
Purchase #3	$40.57	13.208%	$45.9285	$45.93	$45.95	$45.90
Purchase #4	$166.52	13.214%	$188.524	$188.52	$188.50	$188.50
Purchase #5	$162.97	10.336%	$179.8146	$179.81	$179.80	$179.80
Purchase #6	$239.32	5.111%	$251.5516	$251.55	$251.55	$251.60
Purchase #7	$59.49	5.661%	$62.8577	$62.86	$62.85	$62.90
7 purchase totals =	$837.91		$912.7748	$912.77	$912.75	$912.80