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	$156.47	10.833%	$173.4204	$173.42	$173.40	$173.40
Purchase #2	$173.63	3.670%	$180.0022	$180.00	$180.00	$180.00
Purchase #3	$87.84	9.830%	$96.4747	$96.47	$96.45	$96.50
Purchase #4	$155.34	9.436%	$169.9979	$170.00	$170.00	$170.00
Purchase #5	$100.49	11.826%	$112.3739	$112.37	$112.35	$112.40
Purchase #6	$78.26	5.788%	$82.7897	$82.79	$82.80	$82.80
Purchase #7	$160.59	3.736%	$166.5896	$166.59	$166.60	$166.60
7 purchase totals =	$912.62		$981.6484	$981.64	$981.60	$981.70