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	$132.82	7.508%	$142.7921	$142.79	$142.80	$142.80
Purchase #2	$28.34	11.271%	$31.5342	$31.53	$31.55	$31.50
Purchase #3	$125.59	8.111%	$135.7766	$135.78	$135.80	$135.80
Purchase #4	$112.28	13.833%	$127.8117	$127.81	$127.80	$127.80
Purchase #5	$159.79	4.289%	$166.6434	$166.64	$166.65	$166.60
Purchase #6	$174.61	8.127%	$188.8006	$188.80	$188.80	$188.80
Purchase #7	$117.45	8.200%	$127.0809	$127.08	$127.10	$127.10
7 purchase totals =	$850.88		$920.4395	$920.43	$920.50	$920.40