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	$180.93	10.298%	$199.5622	$199.56	$199.55	$199.60
Purchase #2	$148.98	12.443%	$167.5176	$167.52	$167.50	$167.50
Purchase #3	$57.98	9.629%	$63.5629	$63.56	$63.55	$63.60
Purchase #4	$172.63	8.505%	$187.3122	$187.31	$187.30	$187.30
Purchase #5	$64.52	3.278%	$66.635	$66.64	$66.65	$66.60
Purchase #6	$49.78	13.528%	$56.5142	$56.51	$56.50	$56.50
Purchase #7	$86.99	9.615%	$95.3541	$95.35	$95.35	$95.40
7 purchase totals =	$761.81		$836.4582	$836.45	$836.40	$836.50