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	$61.70	6.396%	$65.6463	$65.65	$65.65	$65.60
Purchase #2	$47.58	11.227%	$52.9218	$52.92	$52.90	$52.90
Purchase #3	$224.46	7.783%	$241.9297	$241.93	$241.95	$241.90
Purchase #4	$195.77	7.598%	$210.6446	$210.64	$210.65	$210.60
Purchase #5	$145.86	4.136%	$151.8928	$151.89	$151.90	$151.90
Purchase #6	$217.31	4.493%	$227.0737	$227.07	$227.05	$227.10
Purchase #7	$39.88	9.715%	$43.7543	$43.75	$43.75	$43.80
7 purchase totals =	$932.56		$993.8632	$993.85	$993.85	$993.80