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	$82.32	10.421%	$90.8986	$90.90	$90.90	$90.90
Purchase #2	$159.86	5.586%	$168.7898	$168.79	$168.80	$168.80
Purchase #3	$69.86	6.622%	$74.4861	$74.49	$74.50	$74.50
Purchase #4	$135.85	11.605%	$151.6154	$151.62	$151.60	$151.60
Purchase #5	$218.34	4.715%	$228.6347	$228.63	$228.65	$228.60
Purchase #6	$166.65	7.561%	$179.2504	$179.25	$179.25	$179.30
Purchase #7	$85.37	6.509%	$90.9267	$90.93	$90.95	$90.90
7 purchase totals =	$918.25		$984.6017	$984.61	$984.65	$984.60