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	$222.67	7.601%	$239.5951	$239.60	$239.60	$239.60
Purchase #2	$152.31	13.427%	$172.7607	$172.76	$172.75	$172.80
Purchase #3	$164.55	7.105%	$176.2413	$176.24	$176.25	$176.20
Purchase #4	$151.52	11.318%	$168.669	$168.67	$168.65	$168.70
Purchase #5	$190.79	11.420%	$212.5782	$212.58	$212.60	$212.60
Purchase #6	$38.33	5.369%	$40.3879	$40.39	$40.40	$40.40
Purchase #7	$126.57	8.406%	$137.2095	$137.21	$137.20	$137.20
7 purchase totals =	$1,046.74		$1,147.4417	$1,147.45	$1,147.45	$1,147.50