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	$11.97	13.507%	$13.5868	$13.59	$13.60	$13.60
Purchase #2	$39.88	4.173%	$41.5442	$41.54	$41.55	$41.50
Purchase #3	$78.35	10.577%	$86.6371	$86.64	$86.65	$86.60
Purchase #4	$181.96	10.187%	$200.4963	$200.50	$200.50	$200.50
Purchase #5	$199.83	13.469%	$226.7451	$226.75	$226.75	$226.70
Purchase #6	$134.47	13.487%	$152.606	$152.61	$152.60	$152.60
Purchase #7	$232.43	6.816%	$248.2724	$248.27	$248.25	$248.30
7 purchase totals =	$878.89		$969.8879	$969.90	$969.90	$969.80