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	$132.91	12.338%	$149.3084	$149.31	$149.30	$149.30
Purchase #2	$34.63	9.411%	$37.889	$37.89	$37.90	$37.90
Purchase #3	$138.47	3.105%	$142.7695	$142.77	$142.75	$142.80
Purchase #4	$79.60	3.819%	$82.6399	$82.64	$82.65	$82.60
Purchase #5	$125.65	7.327%	$134.8564	$134.86	$134.85	$134.90
Purchase #6	$51.92	13.339%	$58.8456	$58.85	$58.85	$58.80
Purchase #7	$151.75	5.113%	$159.509	$159.51	$159.50	$159.50
7 purchase totals =	$714.93		$765.8178	$765.83	$765.80	$765.80