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	$240.83	13.719%	$273.8695	$273.87	$273.85	$273.90
Purchase #2	$108.44	13.735%	$123.3342	$123.33	$123.35	$123.30
Purchase #3	$54.64	11.761%	$61.0662	$61.07	$61.05	$61.10
Purchase #4	$76.97	6.402%	$81.8976	$81.90	$81.90	$81.90
Purchase #5	$176.82	3.650%	$183.2739	$183.27	$183.25	$183.30
Purchase #6	$108.68	10.846%	$120.4674	$120.47	$120.45	$120.50
Purchase #7	$64.76	3.494%	$67.0227	$67.02	$67.00	$67.00
7 purchase totals =	$831.14		$910.9315	$910.93	$910.85	$911.00