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	$116.78	12.664%	$131.569	$131.57	$131.55	$131.60
Purchase #2	$237.26	5.562%	$250.4564	$250.46	$250.45	$250.50
Purchase #3	$17.68	10.860%	$19.6	$19.60	$19.60	$19.60
Purchase #4	$184.29	13.208%	$208.631	$208.63	$208.65	$208.60
Purchase #5	$220.28	3.275%	$227.4942	$227.49	$227.50	$227.50
Purchase #6	$72.97	13.485%	$82.81	$82.81	$82.80	$82.80
Purchase #7	$37.32	5.340%	$39.3129	$39.31	$39.30	$39.30
7 purchase totals =	$886.58		$959.8735	$959.87	$959.85	$959.90