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	$75.54	7.808%	$81.4382	$81.44	$81.45	$81.40
Purchase #2	$196.37	3.105%	$202.4673	$202.47	$202.45	$202.50
Purchase #3	$43.94	4.379%	$45.8641	$45.86	$45.85	$45.90
Purchase #4	$101.37	3.213%	$104.627	$104.63	$104.65	$104.60
Purchase #5	$166.44	4.299%	$173.5953	$173.60	$173.60	$173.60
Purchase #6	$105.84	3.481%	$109.5243	$109.52	$109.50	$109.50
Purchase #7	$164.82	5.166%	$173.3346	$173.33	$173.35	$173.30
7 purchase totals =	$854.32		$890.8508	$890.85	$890.85	$890.80