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	$248.98	9.858%	$273.5244	$273.52	$273.50	$273.50
Purchase #2	$158.81	6.312%	$168.8341	$168.83	$168.85	$168.80
Purchase #3	$202.60	7.248%	$217.2844	$217.28	$217.30	$217.30
Purchase #4	$131.72	7.698%	$141.8598	$141.86	$141.85	$141.90
Purchase #5	$180.49	7.448%	$193.9329	$193.93	$193.95	$193.90
Purchase #6	$127.39	11.376%	$141.8819	$141.88	$141.90	$141.90
Purchase #7	$137.32	10.863%	$152.2371	$152.24	$152.25	$152.20
7 purchase totals =	$1,187.31		$1,289.5546	$1,289.54	$1,289.60	$1,289.50