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	$199.57	10.708%	$220.94	$220.94	$220.95	$220.90
Purchase #2	$214.67	9.866%	$235.8493	$235.85	$235.85	$235.80
Purchase #3	$83.54	7.710%	$89.9809	$89.98	$90.00	$90.00
Purchase #4	$125.90	7.110%	$134.8515	$134.85	$134.85	$134.90
Purchase #5	$52.92	11.651%	$59.0857	$59.09	$59.10	$59.10
Purchase #6	$250.55	10.236%	$276.1963	$276.20	$276.20	$276.20
Purchase #7	$136.71	13.301%	$154.8938	$154.89	$154.90	$154.90
7 purchase totals =	$1,063.86		$1,171.7975	$1,171.80	$1,171.85	$1,171.80