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	$86.84	13.859%	$98.8752	$98.88	$98.90	$98.90
Purchase #2	$123.38	11.118%	$137.0974	$137.10	$137.10	$137.10
Purchase #3	$194.81	11.439%	$217.0943	$217.09	$217.10	$217.10
Purchase #4	$75.52	8.587%	$82.0049	$82.00	$82.00	$82.00
Purchase #5	$132.40	12.456%	$148.8917	$148.89	$148.90	$148.90
Purchase #6	$82.76	5.131%	$87.0064	$87.01	$87.00	$87.00
Purchase #7	$135.56	9.113%	$147.9136	$147.91	$147.90	$147.90
7 purchase totals =	$831.27		$918.8835	$918.88	$918.90	$918.90