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	$55.61	4.455%	$58.0874	$58.09	$58.10	$58.10
Purchase #2	$51.86	11.552%	$57.8509	$57.85	$57.85	$57.90
Purchase #3	$80.82	11.280%	$89.9365	$89.94	$89.95	$89.90
Purchase #4	$248.94	7.175%	$266.8014	$266.80	$266.80	$266.80
Purchase #5	$50.27	3.437%	$51.9978	$52.00	$52.00	$52.00
Purchase #6	$200.95	13.386%	$227.8492	$227.85	$227.85	$227.80
Purchase #7	$231.63	13.353%	$262.5596	$262.56	$262.55	$262.60
7 purchase totals =	$920.08		$1,015.0828	$1,015.09	$1,015.10	$1,015.10