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	$209.59	8.553%	$227.5162	$227.52	$227.50	$227.50
Purchase #2	$78.88	4.631%	$82.5329	$82.53	$82.55	$82.50
Purchase #3	$61.41	5.671%	$64.8926	$64.89	$64.90	$64.90
Purchase #4	$141.63	12.455%	$159.27	$159.27	$159.25	$159.30
Purchase #5	$46.45	9.537%	$50.8799	$50.88	$50.90	$50.90
Purchase #6	$143.38	11.562%	$159.9576	$159.96	$159.95	$160.00
Purchase #7	$97.50	3.381%	$100.7965	$100.80	$100.80	$100.80
7 purchase totals =	$778.84		$845.8457	$845.85	$845.85	$845.90