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	$84.41	8.523%	$91.6043	$91.60	$91.60	$91.60
Purchase #2	$85.54	3.802%	$88.7922	$88.79	$88.80	$88.80
Purchase #3	$152.76	12.287%	$171.5296	$171.53	$171.55	$171.50
Purchase #4	$142.32	3.244%	$146.9369	$146.94	$146.95	$146.90
Purchase #5	$164.57	9.539%	$180.2683	$180.27	$180.25	$180.30
Purchase #6	$80.67	9.445%	$88.2893	$88.29	$88.30	$88.30
Purchase #7	$153.47	12.711%	$172.9776	$172.98	$173.00	$173.00
7 purchase totals =	$863.74		$940.3982	$940.40	$940.45	$940.40