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	$151.97	9.631%	$166.6062	$166.61	$166.60	$166.60
Purchase #2	$82.78	9.331%	$90.5042	$90.50	$90.50	$90.50
Purchase #3	$145.38	13.385%	$164.8391	$164.84	$164.85	$164.80
Purchase #4	$157.85	9.801%	$173.3209	$173.32	$173.30	$173.30
Purchase #5	$130.74	3.120%	$134.8191	$134.82	$134.80	$134.80
Purchase #6	$42.76	13.828%	$48.6729	$48.67	$48.65	$48.70
Purchase #7	$217.93	3.153%	$224.8013	$224.80	$224.80	$224.80
7 purchase totals =	$929.41		$1,003.5637	$1,003.56	$1,003.50	$1,003.50