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	$98.98	13.487%	$112.3294	$112.33	$112.35	$112.30
Purchase #2	$165.77	4.748%	$173.6408	$173.64	$173.65	$173.60
Purchase #3	$146.45	4.306%	$152.7561	$152.76	$152.75	$152.80
Purchase #4	$36.28	11.706%	$40.5269	$40.53	$40.55	$40.50
Purchase #5	$75.82	7.493%	$81.5012	$81.50	$81.50	$81.50
Purchase #6	$141.62	7.757%	$152.6055	$152.61	$152.60	$152.60
Purchase #7	$184.66	4.255%	$192.5173	$192.52	$192.50	$192.50
7 purchase totals =	$849.58		$905.8772	$905.89	$905.90	$905.80