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	$17.33	7.575%	$18.6427	$18.64	$18.65	$18.60
Purchase #2	$40.45	6.416%	$43.0453	$43.05	$43.05	$43.00
Purchase #3	$37.25	9.581%	$40.8189	$40.82	$40.80	$40.80
Purchase #4	$133.58	8.212%	$144.5496	$144.55	$144.55	$144.50
Purchase #5	$216.69	11.587%	$241.7979	$241.80	$241.80	$241.80
Purchase #6	$231.63	13.364%	$262.585	$262.59	$262.60	$262.60
Purchase #7	$174.78	8.110%	$188.9547	$188.95	$188.95	$189.00
7 purchase totals =	$851.71		$940.3941	$940.40	$940.40	$940.30