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	$75.36	4.105%	$78.4535	$78.45	$78.45	$78.50
Purchase #2	$95.77	7.687%	$103.1318	$103.13	$103.15	$103.10
Purchase #3	$112.61	6.271%	$119.6718	$119.67	$119.65	$119.70
Purchase #4	$113.42	12.491%	$127.5873	$127.59	$127.60	$127.60
Purchase #5	$88.26	9.468%	$96.6165	$96.62	$96.60	$96.60
Purchase #6	$131.98	7.870%	$142.3668	$142.37	$142.35	$142.40
Purchase #7	$161.97	6.812%	$173.0034	$173.00	$173.00	$173.00
7 purchase totals =	$779.37		$840.8311	$840.83	$840.80	$840.90